Hii, Law - Quality Evolution During Drying of FVFs
6.1. INTRODUCTION
The processing of a food products involves several stages and drying is one such op-
eration that is commonly used in a food manufacturing plant. Quality changes and food
spoilage might occur during drying due to environment that is not always conducive for
processing the food products. Conventionally, food products should be dried below the
level susceptible to growth of microorganism, typically at water activity level of less
than 0.6. Apart from this, product quality is often related to various physical and chemi-
cal parameters, which in many cases, are decided upon by consumers whom will even-
tually purchase and consume it. The governing criteria could be due to taste, colour, tex-
ture, size, shape and the functionality associated with the product. In addition to that,
food manufacturers should also conform to the microbiological and nutritive aspects of
quality control during manufacture.
The aim of this chapter is to provide some general aspects of product quality
attributes associated with the drying of food, vegetable and fruits. The effect of various
drying parameters on product quality is also discussed based on published literature.
6.2. PRODUCT QUALITY ATTRIBUTES
The quality attributes of a dried food product can be classified into physical, chemi-
cal, biological and nutritional (Perera, 2005; Sablani, 2006). The specification of dried
food products also largely depends on these quality attributes. In general, improper
processing conditions results in higher nutritional loss and poorer product quality
(Rahman, 2005).
6.2.1. Physical
6.2.1.1. Colour
Colour is perhaps the most important attribute, apart from product appearance, that
will determine the level of acceptance by consumers. Colour pigments, Maillard reac-
tions and enzymatic browning play significant roles in the colour changes of the product
during drying (Marty-Audouin and Rocha-Mier, 1999). Very often temperature and pH
play an important role during processing as shown in Table 6.1.
Evaluation of colour can be carried out by using destructive or by non-destructive
methods. Destructive method is carried out by evaluating the extracted colour pigments
spectrophotometrically or by using high performance liquid chromatography. Alterna-
tively, the non-destructive method can be used and it is favoured by most researchers.
Using the CIELAB colour space (Lab), the parameters L, a and b values represent
light-dark spectrum with a range from 0 (black) to 100 (white), the green-red spectrum
with a range from -60 (green) to +60 (red), and the blue-yellow spectrum with a range
from -60 (blue) to +60 (yellow), respectively (Abbot, 1999).