Biological Variance in Agricultural Products Experimental Examples

Based on the colour development of tomatoes (theoretical) and apples (measured) as an example the approach to biological variance from a new perspective is made more clear and more explicit. The origin of biological variance is traced back to the stage of maturity at the moment of harvest. By modelling the colour development of individual units in a batch in a generic fashion, and using this model in a non-linear regression analysis on all data from different stages of maturity at harvest, orchards and storage temperatures combined, the effects of biological variance present and its changes in time can be described and predicted. From the analysis it is clear that the most important variable to explain and described variance in colour is the difference between the actual colour and the minimally possible colour for that cultivar. The explained part obtained (well over 95%) is a major indication of the usefulness and applicability of this approach INTRODUCTION In every batch of agricultural produce, a variance is present in all properties. The occurrence of this biological variance is an intrinsic part of the production process. It can originate from a variety of sources like climatic and weather conditions, growing area and soil structure, soil management like fertilisation and ploughing etc. More specific, it is a consequence of variation in the producing sequence as affected by the non-constant external factors like temperature, rainfall and solar radiation. Internal factors, like the level or concentration of compounds and enzymes, will also have an effect on the occurrence and magnitude of biological variance. Up to now, the effects of biological variance have been minimised by sorting and grading on external quality attributes, and by ensuring the external conditions applied are as constant as possible. Only crudely was understood what really happens. For quite some decades, this approach was sufficiently successful. With internal quality attributes (e.g. taste, flavour and aroma) becoming increasingly important to consumers and to trade, time has come to devote our attention to the understanding of the processes that govern the occurrence and behaviour of biological variance in general. Theoretical considerations are presented in Tijskens et al. (2000, 2001). In this paper an example is shown for the decay of the green colour of apples from different growing conditions and picked at different stages of maturity during storage MODELLING BIOLOGICAL VARIANCE Obtaining scientific knowledge is completely based on repeatability of experiments. This means that, except for the temperature dependency, rate constants are independent of the experimental conditions. So, assuming condition-independent rate constants, the variability, observed in our fruits and vegetables, has to be found in the initial conditions of the reactants. For the colour of produce, this is no different. When we follow the development of the colour of individuals in a batch, instead of following the mean colour of a complete batch, we can already detect considerable differences. Generally colour behaves according to a logistic function. Proc. 8 Int. CA Conference Eds. J. Oosterhaven & H.W. Peppelenbos Acta Hort 600, ISHS 2003