Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Enzyme activity and firmness in tomatoes
Tijskens, L.M.M. ; Dijk, C. van - \ 2018
In: Integrated View of Fruit and Vegetable Quality CRC Press - ISBN 1587160196 - p. 73 - 80.

The effect of storage at 3 ‘safe’ temperatures and one chilling temperature on the firmness, water loss and activity of selected enzyme systems (PG) of tomatoes (cv. Tradiro), harvested at two stages of maturity, was experimentally determined. Models built on assumed but plausible reaction mechanisms explain very well the behavior of these product properties as a function of storage temperature and duration simultaneously. Firmness was determined experimentally as the slope and as the compression distance in a flat plate compression test up to a maximum force of 3 N. By using the same fundamental model description both variables, describing tomato texture could be analysed in a combined analysis. It was found that firmness is built up from at least two different type of chemical structures, one decaying mainly at ‘chilling’ temperatures, while the second one decays both at ‘chilling’ and at ‘safe’ temperatures. The percentage variance accounted for was almost 90%. For the activity of polygalacturonase (PG) it was found, that a self initiated autocatalytic production exist. The effect of harvest maturity could be restricted to a different level of initially present activity. The percentage variance accounted for in the statistical analysis, based on the entire dataset simultaneously, was almost 89%.

Mango firmness modeling as affected by transport and ethylene treatments
Schouten, Rob E. ; Fan, Shuang ; Verdonk, Julian C. ; Wang, Yuchen ; Kasim, Nur Fauzana Mohd ; Woltering, Ernst J. ; Tijskens, L.M.M. - \ 2018
Frontiers in Plant Science 871 (2018). - ISSN 1664-462X
Firmness - Kinetic modeling - Mango - Softening - Sources of variation - Sourcing - Transport simulation

More and more, tropical fruit are subjected to accelerated ripening at receiving markets until “ready to eat.” We propose a kinetic model that incorporates the effects of temperature and ethylene on the firmness behavior of “Keitt” and “Kent” mangoes. Stiffness of individual mangoes, as measured by the acoustic firmness tester, was measured repeatedly over time. The firmness model assumes fixed levels of ethylene, established after the climacteric peak, that steadily induces production of softening enzymes that subsequently denaturalize. The initial level of these enzymes is assumed to be zero due to either the tree factor for freshly harvested mangoes, or due to chilling injury for reefer transported mangoes. The kinetic parameter set for “Keitt” mangoes was estimated based on a Spanish batch, freshly harvested and ripened under dynamic temperature scenarios, combined with a reefer transported Brazilian batch stored at four constant temperatures. Firmness data from reefer transported batches, from Brazil, Ivory Coast and Mali, stored at four constant temperatures were used to estimate a set of kinetic parameters for the “Kent” mangoes. Only a partial set of “Kent” kinetic parameters could be established due to the often already advanced stage of softening at the time of arrival. The effect of ethylene was investigated by applying external ethylene levels, varying from 0 to 100 μL L−1. The effect of external application of ethylene was modeled by estimating EF, the ethylene factor, being a reflection of the internal ethylene level and ethylene sensitivity. The effect of ethylene application on softening was sometimes huge. For an Israeli “Keitt” batch a fifty times higher EF was found when the firmness behavior of low- (without ethylene application) and high temperature (with ethylene application) stored sub-batches were compared. However, this effect was sometimes also small, especially for reefer transported mangoes. For commercial application, a reliable prediction of the time until “ready to eat” is not possible because of the current inability to assess EF. Nevertheless, the proposed model described mango softening accurately, irrespective of the sourcing area and includes the effects of storage temperature and ethylene application.

Translucency in cut tomatoes
Tijskens, L.M.M. ; Schouten, R. ; Kooten, O. van; Lana, M.M. - \ 2018
In: Proceedings of the 2nd International Conference on Quality Management of Fresh Cut Produce. - International Society for Horticultural Science (Acta Horticulturae ) - ISBN 9789462612068 - p. 347 - 352.
Appearance - Fresh-cut fruit - Modelling

Translucency is one of the major problems in fresh-cut fruit. This phenomenon affects the use of tomato fruit by the fresh-cut industries. Techniques for measuring translucency are not readily available. As a consequence, the processes that are important in the development of translucency are little understood, let alone described in detail. The colour of produce depends only on the absorption of light by colouring compounds. Translucency does not change the amount of colouring agents in the product, but it does change its appearance by changing the scattering properties. As a consequence the appearance, which is the result of light absorption and scattering combined, is affected by both translucency and colour development. Consumers do buy or reject products based on total appearance. In the short life time of cut fruits, the development of colouring compounds apart from possible oxidation effects will not be very large. Understanding the development of translucency is therefore of major importance for the fresh-cut industry. The development of translucency was visually assessed in tomato slices, obtained from tomatoes at three stages of maturity (mature green, breaker stage and full red) and stored at 5°C. In a second experiment, tomato slices were stored at three temperatures (5, 9 and 13°C) to assess the effects of temperature. In both experiments, non-cut tomatoes were also assessed. The data of both experiments were analysed using a very simple exponential model based on a massive approximation of the mechanism involved. The more precursor is present, the higher the obtainable translucency will be. A model was developed based on this simplified mechanism, and used to analyse all data. The stage of development (maturity) was found to have a major effect on translucency development regulated by the amount of precursor. The rate constant, however, was the same. The temperature only had a minor effect on the rate constant with the same amount of precursor. Explained parts (R2adj) obtained for mean data were well over 97%, for the individual data the explained part was somewhat less.

Firmness behaviour of sliced tomato
Schouten, R. ; Natalini, A. ; Woltering, E. ; Tijskens, L.M.M. - \ 2018
In: Proceedings of the 2nd International Conference on Quality Management of Fresh Cut Produce. - International Society for Horticultural Science (Acta Horticulturae ) - ISBN 9789462612068 - p. 341 - 345.
Kinetic model - Limited compression - Maturity at harvest - PH

Sliced tomatoes soften rapidly as well as becoming translucent. To develop a physiologically-based mechanism to describe softening the firmness of two cultivars, as a function of time, storage temperature, type of compression (repeated on the same spot or single measurements on consecutive spots on the equator of the pericarp) and initial maturity was measured using tomato slices. The proposed mechanism assumes that the softening of slices is radically different from that of whole tomatoes and depends on the stage of ripening at slicing. The mechanism is also based on the assumption that the pericarp solubility will quickly increase because of exposure to, amongst others, vacuolar contents with a low pH. This exposure will have a more serious effect on the firmness behaviour of ripe tomatoes because the pericarp tissue will have been exposed longer to a lower pH environment that will affect pectin solubility. A kinetic model that describes the individual firmness behaviour over time was developed. This model described trends well despite the high variability of the raw data. It was found that firmness loss induced by wounding occurs within 12 h. The effect of the initial maturity on the final firmness of the slices was large. The model indicates that consumer acceptance of sliced tomatoes is greatly affected by selection of cultivars with sufficient final (structural) firmness combined with a thorough assessment of the maturity at the time of slice preparation.

Apples from Monalisa – Biological variation of firmness behaviour in storage and shelf life
Tijskens, L.M.M. ; Schouten, R.E. ; Zanella, A. ; Sadar, N. - \ 2018
In: 8th International Postharvest Symposium. - International Society for Horticultural Science (Acta Horticulturae ) - ISBN 9789462611900 - p. 1415 - 1420.
Attitude - CA storage - Crop load - Probelation - Quantile regression - Shelf-life
Apples are long-term stored in quite similar CA conditions, expecting the behaviour during that storage to be the similar for all apples, only affected by cultivar and picking time. The aim of this study, within the Monalisa project, is the effect of growing conditions on the firmness behaviour of apples during postharvest CA storage and shelf-life. Apples of two cultivars (‘Braeburn’, ‘Kanzi’) were harvested from four orchards (different altitudes and different crop loads) and stored in commercial CA storage for nine months. Samples of 30 apples were taken from CA storage every one or two months and subjected to storage at room temperature. Apples were assessed on firmness shelf-life. Firmness measurements were carried out using the (destructive) puncture test and the (non-destructive) Aweta firmness meter. The first and overwhelming outcome of this study is the huge variation in firmness and the almost absence of firmness decrease of ‘Kanzi’ apples both during CA and shelf-life. The huge variation was tackled by novel statistical analysis techniques (probelation, quantile regression) and assuming a logistic behaviour. Data sets were analysed including the biological variation between individual fruit with explained variation (R2 adj) often over 90%. Only minor effects of the CA duration on the rate of firmness loss during shelf life could be indicated. Altitude has a major effect on the level of firmness while crop load has less effect. Likely, higher altitudes result in lower growing temperatures and therefore in a lower rate of cell division during the early growth phase, which results in smaller and firmer apples. Crop load likely affects the amount of available photo assimilates per fruit. Higher crop load results therefore in smaller and firmer apples. These results clearly show that, up to now, the huge biological variation in the orchard prohibited progress in orchard dependant storage management.
Techniques to assess biological variation in destructive data
Tijskens, L.M.M. ; Schouten, R.E. ; Jongbloed, G. ; Konopacki, P.J. - \ 2018
In: 8th International Postharvest Symposium. - International Society for Horticultural Science (Acta Horticulturae ) - ISBN 9789462611900 - p. 1383 - 1390.
Biological variation - Cross-sectional data - Non-destructive data - Technical variation
Variation is present in all measured data, due to variation between individuals (biological variation) and variation induced by the measuring system (technical variation). Biological variation present in experimental data is not the result of a random process but strictly subject to deterministic rules as found on non-destructive data. The majority of data obtained in research are obtained by destructive techniques. The rules on behaviour and magnitude of variation should however, also apply to these cross sectional data. New techniques have been developed for analysing cross sectional data including the assessment of variation: 1) Probelation. In a set of cross-sectional data, the individual with the highest value at some point in time will resemble the individual with the highest value at previous or future times, and the second highest the second highest at previous times, and so on. One can assign an identification number based on the sorted order of the measured values per measuring point in time. This number can be used as a pseudo fruit number in indexed or mixed effects regression analysis, similar to the data analysis of longitudinal data; 2) Density assessment. For not too complex kinetic processes the density function can be deduced. Measuring a large number of individuals (on a single point in time) provides the possibility to assess directly the variation in the data; 3) Quantile regression. This technique also relies on ranking the data per measuring time. The probelation number is now converted into a probability, and the mean and standard deviation is estimated directly along with the kinetic parameter, using simple non-linear regression. Based on simulated data sets, all three techniques are demonstrated, and the results compared with the input values. Explained parts (R2 adj) obtained are generally well over 90%, provided that the technical variation is not excessively large.
Assessing biological and technical variation in destructively measured data
Tijskens, L.M.M. ; Konopacki, P.J. ; Jongbloed, G. ; Penchaiya, P. ; Schouten, R.E. - \ 2017
Postharvest Biology and Technology 132 (2017). - ISSN 0925-5214 - p. 31 - 42.
Biological variation - Cross-sectional data - Non-destructive data - Statistical analysis - Technical variation

The majority of experimental data are obtained by destructive measuring techniques. Inevitably, in all these data variation is present, sometimes small and negligible, sometimes large, preventing proper analysis and extraction of meaningful information by traditional statistical techniques altogether. In this paper, three systems are presented to analyse destructive (cross-sectional) data, including biological as well as technical variation. The first system involves ranking the data per measuring point in time which provides a pseudo fruit number that can be used in non-linear indexed regression analysis similar as for non-destructive (longitudinal) data. The rationale behind this is that the individual with the highest value at some point in time will resemble the most another individual with the highest value at previous or future times, and the second highest the second highest at previous times, and so on. The second system also relies on this ranking number, but is now converted into a probability, which is used in non-linear regression analysis with quantile functions. The third system is based on optimising the log likelihood of the density function derived from the applied model (i.e., the expected distribution) over the measured data. Simulated data are used to elucidate the power of the three systems. A dataset on mango colour is used to validate the systems on a real-world data set. Although all three systems perform satisfactorily with percentages variability accounted for (R2 adj) well over 90%, a clear preference cannot be given since the choice of the proper analysis system depends on the experimental conditions (number of data, individuals and sampling points in time). Non-linear indexed and non-linear regression with quantile functions delivered the most reliable estimates. The three systems open up the possibility to analyse and reanalyse destructively measured data providing a sufficient large number of individuals and a clear indication of the kinetic model is available.

Assessing the peel colour behaviour of mango 'Nam Dok Mai See Thong' during cool storage
Penchaiya, P. ; Tijskens, L.M.M. - \ 2017
Acta Horticulturae 1154 (2017). - ISSN 0567-7572 - p. 207 - 212.
Appearance - Biological variation - Colour - Quality - Thai mango

Mango 'Nam Dok Mai See Thong' recently became the number-one exported mango of Thailand. It has an attractive appearance, with a golden-yellow peel colour at harvest and slight colour development during ripening. Its peel colour could possibly be used as an indicator for ripeness. Assessing the behaviour of peel colour during storage is the main objective of this research. Mangoes were kept at cool temperature (13°C) for 2 weeks prior moving to ambient temperature in Thailand (28°C). The data set was separated into two groups for non-destructive and destructive tests. In the non-destructive set, peel colour of 108 fruits was measured repeatedly until the quality became unacceptable. In the destructive set, 60 fruits were sampled at random to measure the peel colour and other quality attributes, each time on different fruit. Mangoes from two growing locations were compared. The results showed that peel colour (L∗, a∗, b∗ and Hue) developed gradually during cool storage, but changed drastically after relocation to higher temperatures. The L∗ a∗ and b∗ values and hue angle behaved according to a logistic function. a∗ and b∗ showed an increase, L∗ and hue a decrease. The variation is clearly high at the beginning and decreased gradually during the storage period. Fruit from both the non-destructive and destructive sets showed similar behaviour during storage. The obtained results allow prediction of the behaviour of peel colour during cool storage.

The von Bertalanffy growth model for horticulture : Predicting tomato size at harvest
Tijskens, L.M.M. ; Schouten, R.E. ; Unuk, T. ; Šumak, D. - \ 2017
Acta Horticulturae 1154 (2017). - ISSN 0567-7572 - p. 33 - 39.
Biological variation - Size distribution - Size prediction

Traditionally, crop load and fruit yield from previous seasons are used as indicators for prediction of fruit size. Disregarding the inevitable biological variation between fruit, von Bertalanffy (1938) described the growth, expressed as length, of virtually any living organism. The model is here extended to include the variation between individuals in a batch. Using this extended model, fruit size and its variation can be predicted, using measurements of a large number of fruit at a single point during early development. The diameter of 200 tomatoes was measured 15 days after full bloom (DAFB). Using the density function derived from the extended von Bertalanffy model, and applying prior knowledge of some of the model parameters, the variation in size at harvest could be predicted. Validation of the results was obtained by comparing the predicted sizes with the diameters of the same tomatoes at harvest.

Development and distribution of quality related compounds in apples during growth
Sadar, N. ; Urbanek Krajnc, A. ; Tojnko, S. ; Tijskens, L.M.M. ; Schouten, R.E. ; Unuk, T. - \ 2016
Scientia Horticulturae 213 (2016). - ISSN 0304-4238 - p. 222 - 231.
Apple - Biopsy sampling - Colour - Modeling - Organic acids - Sugars - Taste

Colour and taste are important attributes of apple fruit quality and have therefore been widely studied. Nevertheless, because of the destructive sampling methods commonly used to obtain the data, and of the subsequent traditional analyses, ignoring the effects of biological variation, the knowledge on the kinetic mechanisms of synthesis and degradation of individual quality components during fruit development and growth is still lacking. Spatio-temporal changes of taste components (sugars: fructose, sucrose, glucose, organic acids: malic, citric, shikimic and fumaric acid) and colour aspects (a) in individual apple fruits were monitored to assess the dynamics and mechanisms of change during development and ripening with respect to location within fruit as a factor and the variation between individual apples. Data were analysed with non-linear indexed regression based on either a logistic or an exponential process oriented model assessing the technical variation simultaneously. The rate constants for colour or taste component were roughly similar between cultivars, suggesting a similar mechanism of development and confirming the generic nature of the model. There was a very large biological variation in individual quality components observed in the raw data (the biological variation), which can be almost exclusively explained by the difference in the maturity stage between individual fruit. The explained parts (R2 adj) were, with one exception, higher than 0.90. The major contribution of this study is the fact that all the herein monitored taste defining components can be analysed and described with the same process-oriented model.

Modelling the colour of strawberry spread during storage, including effects of technical variations
Kadivec, Mirta ; Tijskens, Pol ; Kopjar, Mirela ; Simčič, Marjan ; Požrl, Tomaž - \ 2016
Polish Journal of Food and Nutrition Sciences 66 (2016)4. - ISSN 1230-0322 - p. 271 - 276.
colour - modelling - strawberry spread - technical variation

The colour of freshly processed strawberry spread changes relatively rapidly from a bright red to a dull red, which then makes its appearance generally less acceptable for consumers. The colours of strawberry spreads following several processing conditions were measured under different storage conditions. Additional sugar and colorant had only slight effects on the colour decay, while exclusion of oxygen and daylight did not affect this process. The only condition that clearly maintained the freshly processed appearance was storage at 4°C. Hexagonal bottles were filled with the strawberry spreads and their colour was repeatedly measured at the six sides of the bottles, using a Minolta chroma meter. Data were analysed using non-linear indexed regression analysis based on a logistic function for the three colour aspect of a∗, b∗ and L∗. This technology allowed the determination of the variation in these data in terms of improved reliability (R2 adj, >90%). It also allowed better interpretation of the processes involved. All variations in the data could be attributed to technical variation.

Salinity and ripening on/off the plant effects on lycopene synthesis and chlorophyll breakdown in hybrid Raf tomato
Sánchez-González, María J. ; Schouten, Rob E. ; Tijskens, L.M.M. ; Cruz Sánchez-Guerrero, M. ; Medrano, Evangelina ; Rio-Celestino, Mercedes del; Lorenzo, Pilar - \ 2016
Scientia Horticulturae 211 (2016). - ISSN 0304-4238 - p. 203 - 212.
Colour physiology - Maturity - Remittance spectroscopy - STAY-GREEN proteins

The aim of this study was to describe the physiology of fruit colour in tomato as affected by salinity and ripening on and off the plant. Chlorophyll and lycopene levels were repeatedly measured in ninety Raf tomatoes over a period of eight days using remittance spectroscopy. Fruits were subjected to three salinity levels and were measured either on or off the plant. The physiology of tomato colour was described by a kinetic model centred on the role of STAY-GREEN proteins (SGR) that was calibrated simultaneously on chlorophyll and lycopene data with a percentage variance explained for of 91%. Lycopene precursor and transcript SGR levels were estimated considerably higher for on-plant than for off-plant ripened fruits which indicates ongoing expression while attached to the plant. There is less inhibition of the lycopene precursor by SGR in on plant ripened tomatoes which results in higher maximum lycopene levels and less chlorophyll breakdown causing residual chlorophyll levels. Effects of salinity treatments on chlorophyll breakdown and lycopene synthesis are small, but higher salinity levels strongly diminish fresh weight. Ripening on and off the plant strongly affects colour physiology of tomato fruit and is described well by the proposed model.

From fruitlet to harvest : Modelling and predicting size and its distributions for tomato, apple and pepper fruit
Tijskens, L.M.M. ; Unuk, T. ; Okello, R.C.O. ; Wubs, A.M. ; Šuštar, V. ; Šumak, D. ; Schouten, R.E. - \ 2016
Scientia Horticulturae 204 (2016). - ISSN 0304-4238 - p. 54 - 64.
Apples (Malus domesticus, borkh) - Biological variation - Diameter - Length - Peppers (Capsicum annuum L. - Size prediction - Tomatoes (Solanum lycopersicum L. - Volume - Von bertalanffy growth model

Size is an important property of all fruit as it determines, together with crop load, fruit yield. The aim of this study is to model the increase in fruit size during cell expansion based on diameter or length and to predict fruit size and volume, including the variation in size and volume, at harvest. The size of individual fruit during growth of fruit (four apple, two tomato and six pepper cultivars) was measured from early fruit set until harvest at several seasons. Size data were evaluated as diameter and length using the von Bertalanffy growth model, adapted to include the variation in size between individuals and the effect of growing temperature. The adapted von Bertalanffy model describes the increase in diameter and length and their variation. For any fruit type, size increased along the same generic growth model. A single stochastic variable, the biological shift factor, was sufficient to describe the variation in development time, initial size and maximum size. For all batches the percentage variation explained for were well over 93% with growth rate constants similar per species and only a minor effect of growing temperature.Prediction of the maximum size distribution based on measurements half way the cell expansion period is explored and discussed. Size and its distribution can be predicted based on a single measuring point in time but with two or three points in time the prediction system becomes more robust.

Sugar and acid interconversion in tomato fruits based on biopsy sampling of locule gel and pericarp tissue
Schouten, R.E. ; Woltering, E.J. ; Tijskens, L.M.M. - \ 2016
Postharvest Biology and Technology 111 (2016). - ISSN 0925-5214 - p. 83 - 92.
This study deals with quantifying sugar and acids levels important for the perceived taste of tomatoes (Solanum lycopersicum). Sugar and acids levels were measured repeatedly on the same tomato using tissue samples obtained with a biopsy needle in combination with HPLC protocols. Biopsies of pericarp and locular gel tissue from tomatoes differing in position in the truss, from mature green to ripe red, were taken from a beef- (‘Licorossa’), a cocktail- (‘Lucino’) and a cherry type (‘Petit Sweet’) cultivar. Tomatoes were stored up to three weeks at three temperatures (12, 19 and 24.5 °C) and biopsy samples were taken every few days. A model regarding the most important processes that interconvert sugars and acids (glycolysis, TCA cycle and gluconeogenesis (GNG)) is proposed. Results of the model calibration showed more breakdown of hexoses in red tomatoes and more conversion of malate into hexoses in green tomatoes. More hexose turnover was found in locular gel than in pericarp tissue. GNG was more important in the cherry type cultivar due to faster hexose and malate breakdown. In the round type cultivar malate levels were higher due to faster citrate breakdown and slower malate breakdown. Starch and sucrose levels did not significantly affect postharvest sugar and acid development. Molecular markers that quantify the kinetic parameters of the model might be important to develop genotypes with better taste performance.
A Case Study of a Decision Support System on Mango Fruit Maturity
Walsh, K.B. ; Subedi, P. ; Tijskens, L.M.M. - \ 2015
Acta Horticulturae 1091 (2015). - ISSN 0567-7572 - p. 195 - 204.
Mango fruit maturity can be difficult to determine from external attributes. Assessment of parameters of fruit on tree (dry matter, internal flesh colour) relevant to estimation of fruit maturity was undertaken with a handheld (near infrared spectroscopic) system. Measurement error on dry matter was low (typical RMSEP 0.6% DM). Repeated measurements on the same individual fruit from 78 different blocks across two farms demonstrated that each piece of fruit was on a similar, but individual, maturation trajectory, with a time offset. The offset was presumably related to date of pollination or environmental conditions around the fruit (e.g., inner or outer canopy). A non-linear indexed regression model, coupled with the use of a ‘biological shift factor’, was used to describe the time series data. Estimated biological shift factors were larger for dry matter than flesh colour, indicative of an earlier change in dry matter, albeit at a lower rate. Differences between blocks within a farm and between two farms were small, indicating the maturation processes were independent of local conditions. This technique could be used to trace the source of variation within a block (e.g., to location in canopy or plant water status), towards the goal of reducing this variation, leading to crops of greater uniformity.
Harvesting quality, Where to start?
Tijskens, L.M.M. ; Schouten, R.E. ; Walsh, K.B. ; Zadravec, P. ; Unuk, T. ; Jacob, S. ; Okello, R.C.O. - \ 2015
In: Acta Horticulturae International Society for Horticultural Science (Acta Horticulturae ) - ISBN 9789462610965 - p. 269 - 276.
Acids - Biological variation - Dry matter content - Fruit size - Sugars

Size increase (expressed as diameter) of four apple cultivars in five seasons during about 130 days before harvest, was analysed with a simple first order production mechanism. All variation in diameter among individual fruit could be attributed to the same origin (development stage or biological age), with explained parts (R2 adj) of more than 98%. The same general behaviour of diameter development was observed in two tomato cultivars whose fruits where grown at two different temperatures. These data were also analysed using the same model with explained parts (R2 adj) of about 90%. Converting diameter into volume (assuming a perfect sphere), the usually observed asymmetrical sigmoidal behaviour was obtained, frequently described in growth modelling with the Richard's curve. A similar sigmoidal behaviour was also observed in the accumulation of dry matter (DM), as measured with NIR technology in growing mangoes. The cubic root of these data on DM could be analysed using the same model formulation, including the variation between individual fruit, with R2 adj well over 90%. Accumulation of DM ends at harvest, so the mechanism of DM production can very well define the final level of DM obtained in harvested fruit. Since sugars and DM are strongly related (e.g., conversion of starch into sugars, Brix values), a very similar mechanism could govern the accumulation of sugars. Destructively measured data on sugars were collected in nectarines, showing indeed a very similar overall behaviour and variation. This indicates that growth (diameter, mass) and quality increase (DM, sugars) could be described by a very similar mechanism, providing the first tools in the quest to harvest quality.

Measurement of mango firmness by non-destructive limited compression technique
Penchaiya, P. ; Uthairatanakij, A. ; Srilaong, V. ; Kanlayanarat, S. ; Tijskens, L.M.M. ; Tansakul, A. - \ 2015
Acta Horticulturae 1088 (2015). - ISSN 0567-7572 - p. 73 - 78.
Compression - Firmness - Mango - Non-destructive quality evaluation

Thai mango 'Nam Dok Mai Si-Thong' has an attractive golden yellow skin colour even in immature fruit, not ready for consumption. Firmness becomes an important quality attribute to assess the ripening stage of the fruit during storage. In this study, the possibility of a non-destructive method using a texture analyser for assessing the firmness behaviour during storage was investigated in three different experiments for (1) probe selection, (2) distance selection using the selected probe and (3) evaluation of the selected probe and distance on mango quality. The results revealed that an aluminium flat probe with 35 mm diameter is a suitable probe for measurement. Limited distance compression at 1 mm was selected since that combination did not leave any compression marks on the fully ripened mangoes. Evaluation of mango quality attributes obtained by this technique could be used to assess non-destructively the firmness behaviour of the mango fruit during storage. The technique can be used to monitor the firmness of mango fruit on an individual basis, using the same fruit in successive assessments. Non-linear indexed regression can be applied to extract information on the behaviour and variation of firmness of individual mangoes. Obtained explained parts (R2 adj) frequently are well over 90%.

Taste and appearance in the supply chain, where to start? spatial distribution of colour, sugars and acids in growing apples
Sadar, N. ; Tijskens, L.M.M. ; Urbanek Krajnc, A. ; Tojnko, S. ; Unuk, T. - \ 2015
Acta Horticulturae 1091 (2015). - ISSN 0567-7572 - p. 21 - 28.
Appearance - Apples - Growth - Organic acids - Spatial distribution - Sugars - Taste

Samples were taken from apple flesh while at the tree ('Gala' and 'Pinova') using a biopsy sampling system. After sampling the wound was closed with vaseline, which prevented wound responses. Samples were taken at different times over the circumference of the apples (at about 70 above the equator) to monitor the spatiotemporal distribution of acids (malic, citric, fumaric) and sugars (glucose, fructose and sucrose). At the same time the skin colour was assessed with a Minolta colour meter at the same location. The distribution over the circumference of the apples revealed for both cultivars a sinusoidal pattern for all colour aspects and for citric acid, while only fructose in 'Gala' showed a clear sinusoidal pattern. For all other variables measured, the pattern was only faint, with a low amplitude. Although the system is still prone to a large measuring error, biopsy sampling is a powerful tool to study the spatio-temporal distribution of taste components.

Dynamics of Firmness and Colour of Thai Mango Cultivar 'Nam Dok Si-Thong'
Penchaiya, P. ; Tijskens, L.M.M. ; Uthairatanakij, A. ; Srilaong, V. ; Tansakul, A. ; Kanlayanarat, S. - \ 2015
Acta Horticulturae 1091 (2015). - ISSN 0567-7572 - p. 261 - 266.
Firmness and colour of Thai mango (‘Nam Dok Mai Si-Thong’) were assessed
(firmness at two opposite sides) at regular intervals during storage at 13°C for
14 days, followed by storage at 28°C for another 8 days. The mangoes were
individually labelled and the obtained data were analysed using a logistic decay for firmness and all colour attributes (L*, a*, and b*), including the biological variation within in a batch. The variation in maturity was expressed as biological shift factor. Explained parts of around 90% were obtained for all variables. The biological shift factors are normally distributed. No major difference was found for firmness between both sides of the mangoes. Hardly any relation was found between the biological shift factors of the colour attributes with that of firmness. That confirms that (skin) colour cannot be used to assess the maturity status of firmness in this cultivar. As expected, a pronounced effect of temperature was found, but only on the rate constant of the softening and colour decay process. At 28°C, softening was almost 1.65 times faster and colour development 5 times faster for a* and b* colour aspects than at 13°C. The other model parameters and the model structure were, however, not affected by temperature. That means that in the supply chain, the same model can be used to assess and predict the behaviour of colour and firmness in the entire chain.
Green mathematics: Benefits of including biological variation in your data analysis
Tijskens, L.M.M. ; Schouten, R.E. ; Unuk, T. ; Simcic, M. - \ 2015
Acta Agriculturae Slovenica 105 (2015)1. - ISSN 1581-9175 - p. 157 - 164.
Biological variation is omnipresent in nature. It contains useful information that is neglected by the usually applied statistical procedures. To extract this information special procedures have to be applied. Biological variation is seen in properties (e.g. size, colour, firmness), but the underlying issue is almost always to the variation in development or maturity in a batch of individuals generated by small scale environmental differences. The principles of assessing biological variation in batches of individuals are explained without putting emphasis on mathematical details. Obtained explained parts increase from about 60 to 80 % for the usual approach to 95 when the biological variation is taken into account. When technical variation or measuring error is small even 99 % can be achieved. The benefit of the presented technology is highlighted based on a number of already published studies covering the colour of apples during growth and storage and the firmness of cut tomatoes during storage.
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