IWT-Peter Ragaert 2002

Modelling microbiological and physiological factors affecting total quality of minimally processed fruits and vegetables

Minimally processed fruits and vegetables are becoming more popular in the last decades because of their good degree of freshness, their convenience, their high nutritional value and their lack of preservatives.
In this project, the focus will be on packaged shredded mixed lettuce and packaged strawberries. The quality of those products is determined by a lot of factors like texture, colour, taste and flavour. All of these quality factors can be measured both sensorial (by means of a trained taste panel) and instrumental (by means of different instruments or methods). Examples of these latter measurements include colorimetry and texturometry (which are physical factors), total acidity, suspended solids and chromatography (HPLC-GC) (which are chemical factors).
During the storage period of the minimally processed fruits and vegetables, the quality is influenced by two major processes: physiological degradation, due to enzymatic activity of the plant tissue itself (such as respiration) and microbiological degradation, due to the presence of different micro-organisms on the plant. These latter are not removed from the tissue during processing because of the minimal handling of the produce such as shredding and washing.
It is the aim of the project to determine the role of these two processes by following the evolution of the different quality factors as mentioned above, both instrumental and sensorial. The focus will be on the behaviour of the different micro-organisms by inoculating them on irradiated packaged shredded mixed lettuce and irradiated packaged strawberries. The evolution of the quality factors will be modelled, as shown in Fig. 1.

As mentioned above, quality will change during storage due to a combination of physiological and microbiological degradation. This is observed by changes in chemical and physical factors (or conditions). These conditions are indicated with X in Fig. 1.
The changes of physiological quality can be described as a function of changes of certain physical and chemical conditions (Xp). These conditions are a function of time, temperature, composition of the atmosphere inside the package and the initial value of these conditions, measured on day 0 (Xp,0) (day 0 : packaging day).
The quality is also determined by the behaviour of different micro-organisms, present on the packaged fruit or vegetable. Certain physical and chemical conditions (Xm) will undergo some changes, dependent on the initial value of these conditions (Xm,0) and on the number of micro-organisms. This number is dependent on time, temperature, composition of the atmosphere inside the package and the initial count of micro-organisms, present or inoculated on day 0.
Part of the observed changes of physical and chemical conditions can be described by certain physical, chemical, biological (or microbiological) rules (Xwb: white box). Another part probably will have to be described with empirical rules (Xbb: black box). Time, storage temperature and the atmosphere inside the package will be considered as input of the model.
The measurements of the quality factors (or conditions), as mentioned above, will result in values yi (in the case of instrumental measurements) and in values ys (in the case of sensorial measurements with a trained taste panel). The relation between the conditions and the values is indicated with the outputrelations hi en hs respectively. In this project, the relation between instrumental and sensorial measurements will also be investigated. This is indicated in Fig. 1 with g. By doing so, quality could be predicted in an instrumental way.

In this project, the characterization of the microbiological spoilage will contribute to a better knowledge of the behaviour of the typical microflora of the minimally processed fruits and vegetables, as in the past, little attention has been given to this aspect. By modelling different quality factors, quality of the produce and the time that the produce is still acceptable for consumption are defined more accurate. If one of the factors exceeds a certain limit of acceptance for the consumer, the produce will be disapproved, even if the other quality factors are still acceptable. The relative importance of the different quality factors as perceived by consumers and as measured with both sensorial and instrumental methods will be determined by inquiries to the consumers, which is also a part of this project. This will give better insight in the factors that influence the consumers' perception towards these minimally processed fruits and vegetables.

Project duration: 2002-01-01 - 2005-12-31

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Peter Ragaert
Department of Applied Mathematics, Biometrics and Process Control
Coupure Links 653
9000 Gent
Tel: +32(0)9 264 61 41
Fax: +32(0)9 225 55 10
Email: Peter.Ragaert@ugent.be

Last update: 01 december 2008, webmaster@biomath.ugent.be

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