wow! Thank you! Those are VERY useful links! I am grateful!
Well I don't know much about garlic and I also don't know how you process the garlic in your factory. I suppose that you are dehydrating them after cutting and blanching them. With a quick search I found some general information (below). Nothing directly related with color formation though... If you do cut, blanch and dehydrate them then I suppose that the enzyme responsible for the enzymic browning is not totally deactivated during blanching. Do you dip them in any solution? Unfortunately I am not aware of the chemical composition of garlic or the enzymes that are responsible for enzymatic browning in garlic. I suppose it could be polyphenoloxidase as well but I am not sure.
The following refer to drying processing:
Organoleptic quality is severely affected during drying since color and flavor are the most important sensory attributes of dried foods. The development of color due to enzymatic and non-enzymatic browning is one of the major problems that occurs during the processing and storage of dehydrated foods. Browning reactions also produce off-flavor development and loss of nutritional value. Enzymatic browning is due to the effect of enzymes that catalyze the hydroxylation and oxidation of phenolic compounds. Nonenzymatic browning is a Maillard reaction involving amino groups and reducing sugas that result in brown polymeric pigments. The rates of both types are strongly influenced by composition, temperature, water activity and pH.
The development of color in different foods has been extensively studied. Although several mathematical models have been proposed, in most cases a zero-order reaction with or without an induction period or a first-order reaction has been found to describe the kinetics of browning. The effects of temperature and moisture content on the reaction rate constant for color changes in onion and garlic that follow pseudo first-order kinetics are shown in Figure 11-3.
Figure 11-3 (page 139).
Chemical and thermal treatments such as sulfating or blanching are used to control enzymatic browning by enzyme inactivation in fruits and vegetables. However, thermal treatment is not recommended in products such as onion and garlic where some desirable enzymatic reactions involved in the production of the characteristic flavor and pungency are required. The enzyme inactivation reactions and loss of pungency can be modeled by first-order kinetics.
Since the stability of pigments in foods is affected by many factors, their degradation follows complex mechanisms which do not follow the same kinetics. However, most important degradation reactions such as chlorophyll, anthocyanins and carotenoids have been reported to follow pseudo first-order kinetics (Crapiste, 2000).
Dehydration technology:
(step 4) Cutting and rinsing:
Based on product requirements, raw materials can be cut into definite shape and size to facilitate dehydration. In general, vegetables are cut into slices, strips, dices and shreds, either mechanically or by hand. For some vegetables such as scallions and garlic, cutting has to be accompanied by continious rinsing to remove the colloidal liquid (cytoplasm) due to cutting to facilitate dehydration and provide products with good color and appearance.
(step 6) Color protection:
For vegetable products that change color easily, the addition of harmless color protectants such as sodium bicarbonate or citric acid (in the blanching water) may be permitted. The residual liquid on the vegetable must be removed by centrifuge (Cai et al., 2003).
G.H. Crapiste, Qualite Changes in Foods During Drying, Trends in Food Engineering, E. Lozano, Cristina Anon, CRC Press, 2000.
Tongyi Cai, Fang Chen and Jinghua Qi, Dehydrated Oriental Mushrooms, Leafy Vegetables and Food Preparation Herbs and Condiments, Handbook of Vegetable preservation and Processing, Yiu H. Hui, Sue Ghazala, Dee M. Graham, K. D. Murrell, Wai-Kit Nip, CRC Press, 2003.
I will search more when I 'll have more time!
Thank you again for your help!
Cheers!
Edited by SaRaRa, 17 January 2009 - 04:00 PM.