Maarten Hertog

A dynamic and generic model of gas exchange of respiring produce: the effects of oxygen, carbon dioxide and temperature

Abstract A generic model is developed that describes rates of respiration and fermentation, in response to temperature and environmental gas conditions (oxygen and carbon dioxide). The mathematics of the model are based on Michaelis–Menten kinetics. Respiration is simplified as the effect of one enzymic reaction, inhibited by its own product, carbon dioxide. Both competitive, and uncompetitive inhibition are incorporated. Fermentation is modelled including the competitive inhibition of fermentation by both oxygen and carbon dioxide. Temperature dependence is introduced using Arrhenius equations for the maximum rates of oxygen consumption and carbon dioxide production. The model is generic in nature: it is applicable to different types of products (apple, chicory and tomato) at different conditions (in terms of O2, CO2 and temperature) and for different types of inhibition. This fitness is an indirect validation of the assumptions on which the model is based.

POSTHARVEST SOFTENING OF APPLE (MALUS DOMESTICA) FRUIT: A REVIEW

Abstract Postharvest softening of apple (Malus domestica (Borkh.)) fruit is a serious problem for growers in many countries, including New Zealand. To reduce this problem considerable research has been undertaken to determine the biological causes of softening so that this process can be managed or controlled more effectively. This review describes the pattern of softening for harvested apple fruit, and how it is influenced by different preharvest, at‐harvest, and postharvest factors. Information is also given on the likely physiological and biochemical causes of apple softening, such as fruit anatomy and cell packing, modification of the cell wall and membranes, changes in cell turgor, and the role of ethylene and other growth regulators. Despite many softening studies, there is still a poor understanding of what causes firmness variation in the marketplace. Until this understanding is improved, apple producers will continue to struggle to meet market requirements for texture.

Food process modelling.

Part 1 Principles of modelling: Fundamental approaches: Power and pitfalls of deductive modelling Problem decomposition Kinetic modelling Modelling of heat and mass transfer Combined discrete/continuous modelling. Part 2 Principles of modelling: Empirical approaches: Power and pitfalls of inductive modelling Data mining Modelling and prediction in an uncertain environment. Part 3 Applications: Agricultural production: Yield and quality prediction of vegetables Modelling and management of fruit production Dairy production Beef cattle production. Part 4 Applications: Processing technologies: Use of models in process development: the case of fermentation processes Improving modified atmosphere packaging through conceptual models Modelling thermal processes: cooling and freezing Modelling thermal processes: heating. Part 5 Applications: Safety and quality in the food chain: Modelling food quality Modelling microbiological safety Modelling use of time-temperature indicators in distribution and stock rotation Modelling the management of distribution centres Concepts of chain management and chain optimisation.

The effects of temperature and senescence on the accumulation of reducing sugars during storage of potato (Solanum tuberosum L) tubers: A mathematical model

Abstract A dynamic mathematical model based on underlying physiological processes is developed to describe, analyze and predict the storage behaviour of potato ( Solanum tuberosum L.) tubers in terms of accumulation of reducing sugars. The data necessary for calibration and validation of the model were gathered during long term storage experiments over a wide range of storage temperatures for several seasons and cultivars. Although the model is based on a considerable simplification of the occurring physiological processes, it is capable of accounting for about 95% of the storage behaviour, including both cold-induced and senescent sweetening. The concept is postulated that the state of maturity at time of harvest determines storage behaviour through the initial amount of enzyme (or enzyme system) responsible for cold-induced sweetening.

The impact of biological variation on postharvest population dynamics

Abstract This paper outlines a mathematical approach to the interpretation of postharvest batch behaviour based on the underlying processes occurring at the level of the individual food items and on the amount of biological variation present. This technique opens the door to a mechanistic interpretation of postharvest batch behaviour, both qualitative and quantitative, enabling the postharvest industries to improve their control of the quality of their produce throughout the postharvest chain. The generic approach is outlined and applied to case studies on shrivelling of ‘Braeburn’ apples, the colour change of ‘Hass’ avocados and stress crack development in corn grains.

Protocol: An updated integrated methodology for analysis of metabolites and enzyme activities of ethylene biosynthesis

BackgroundThe foundations for ethylene research were laid many years ago by researchers such as Lizada, Yang and Hoffman. Nowadays, most of the methods developed by them are still being used. Technological developments since then have led to small but significant improvements, contributing to a more efficient workflow. Despite this, many of these improvements have never been properly documented.ResultsThis article provides an updated, integrated set of protocols suitable for the assembly of a complete picture of ethylene biosynthesis, including the measurement of ethylene itself. The original protocols for the metabolites 1-aminocyclopropane-1-carboxylic acid and 1-(malonylamino)cyclopropane-1-carboxylic acid have been updated and downscaled, while protocols to determine in vitro activities of the key enzymes 1-aminocyclopropane-1-carboxylate synthase and 1-aminocyclopropane-1-carboxylate oxidase have been optimised for efficiency, repeatability and accuracy. All the protocols described were optimised for apple fruit, but have been proven to be suitable for the analysis of tomato fruit as well.ConclusionsThis work collates an integrated set of detailed protocols for the measurement of components of the ethylene biosynthetic pathway, starting from well-established methods. These protocols have been optimised for smaller sample volumes, increased efficiency, repeatability and accuracy. The detailed protocol allows other scientists to rapidly implement these methods in their own laboratories in a consistent and efficient way.

Treatment of missing values for multivariate statistical analysis of gel‐based proteomics data

The presence of missing values in gel‐based proteomics data represents a real challenge if an objective statistical analysis is pursued. Different methods to handle missing values were evaluated and their influence is discussed on the selection of important proteins through multivariate techniques. The evaluated methods consisted of directly dealing with them during the multivariate analysis with the nonlinear estimation by iterative partial least squares (NIPALS) algorithm or imputing them by using either k‐nearest neighbor or Bayesian principal component analysis (BPCA) before carrying out the multivariate analysis. These techniques were applied to data obtained from gels stained with classical postrunning dyes and from DIGE gels. Before applying the multivariate techniques, the normality and homoscedasticity assumptions on which parametric tests are based on were tested in order to perform a sound statistical analysis. From the three tested methods to handle missing values in our datasets, BPCA imputation of missing values showed to be the most consistent method.

Physical change in apple texture with fruit temperature: effects of cultivar and time in storage

Abstract Flesh firmness is used to assess apple (Malus domestica Borkh.) quality both before and after low temperature storage. The effect of fruit temperature on apple firmness at different times during postharvest handling is not known. Experiments were conducted to quantify physical change in apple texture readings with change in fruit temperature. ‘Royal Gala’, ‘Granny Smith’, and ‘Pacific Rose™’ apple fruit were stored at 0°C, while ‘Coxs Orange Pippin’ was stored at 3°C. At different times during storage, flesh firmness and cortical tensile strength were measured on fruit at storage temperature, after 24 h at 20°C, or after 24 h at 20°C followed by 24 h at the storage temperature. ‘Royal Gala’, ‘Granny Smith’ and ‘Coxs Orange Pippin’ fruit had higher firmness readings at harvest when measured at 20°C than at 0–3°C, but after 50–100 days at 0–3°C firmness and tensile strength readings were greater when measured at 0–3°C than at 20°C. ‘Pacific Rose™’ had similar firmness and tensile strength readings when measured at 0°C and 20°C. ‘Royal Gala’ and ‘Coxs Orange Pippin’ were measured for firmness at different fruit temperatures at harvest and after storage. The relationship between firmness readings and fruit temperature between 0 and 20°C was linear and positive at harvest and linear and negative for stored fruit. Firmness change with temperature was not affected by orchard or harvest maturity. These results suggest that physical changes in firmness with fruit temperature are common for the cultivars studied, and thus could be used to compare firmness values for fruit from different orchards that were measured at different temperatures.

Activity of pectin methyl esterase during blanching of peaches

The activity of pectin methyl esterase (PE) in peaches during blanching treatments was modelled and analysed. It was postulated that the enzyme exists in two configurations, one bound and one soluble. The bound configuration can be converted into the soluble configuration. These two configurations have a different susceptibility to temperature. All rate constants of reaction were modelled as dependent on temperature according to the Arrhenius law. Despite the daily measuring variance, the variance accounted for by the model in multivariate nonlinear regression analysis was more than 90%. The obtained parameter values were highly comparable for two consecutive seasons. An analysis of the data of the two seasons combined was feasible with the kinetic parameters estimated in common, without losing information with a tremendous increase in predictive power.

Nondestructive Measurement of Fruit and Vegetable Quality

We review nondestructive techniques for measuring internal and external quality attributes of fruit and vegetables, such as color, size and shape, flavor, texture, and absence of defects. The different techniques are organized according to their physical measurement principle. We first describe each technique and then list some examples. As many of these techniques rely on mathematical models and particular data processing methods, we discuss these where needed. We pay particular attention to techniques that can be implemented online in grading lines.