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Analysis of free galactose contents during cold storage of four apple cultivars, in thermally treated apples and green beans, and in clear apple juices produced using different enzymatic aids Jim, Vickie Jin Wai

Abstract

Dietary control of galactose is the only recourse available to patients with galactosemia because there is no cure or drug that can control the disease. However, it is impossible to eliminate all sources of galactose because it is widely available in foods. Fruits and vegetables, which were previously considered to be safe for consumption, have been shown to contain small but significant amount of galactose that can cause complications. Currently, there is limited information on how extended storage and different processing techniques can affect the free galactose content in fruits and vegetables. Therefore, this research investigated how free galactose is affected by cultivar difference and storage time in 4 varieties of apples; thermal processing in apples and green beans; and enzymatic preparations used in clear apple juice production. Sugars were extracted from produce with 80% ethanol and free galactose contents was determined by gas chromatography where galactose and other sugars were derivatized into oxime-trimethylsilyl derivatives for monosaccharides and trimethylsilyl derivatives for sucrose before analysis. Different cultivars of apples were shown to have different free galactose contents and to exhibit different characteristics in changes in amount of free galactose during the 9-month storage. Red Delicious and Braeburn apples did not show significant increase in free galactose concentration over the course of the 9-month storage period. Spartan and Fuji showed increase after 3 and 6 months of storage respectively and the increases persisted until the end of the storage study. Blanching caused leaching of free galactose into the processing water and canning to commercial sterility partially solubilized pectin polymers and release galactose from the pectin side chains but the liberated galactose was also solubilized into processing water, therefore, free galactose concentration in the plant tissue decreased. Canning to double commercial sterility increased the free galactose concentration in plant tissue. This may have been due to the release of galactose from hemicellulosic polysaccharides at this increased thermal treatment, and its entrapment inside the cellulosic matrix of the plant cell wall. The use of a liquefaction enzymatic preparation in clear apple juice production caused the free galactose content in the apple juice increased by 14.62mg /100mL compared to the control juice because cell wall polymers were completely broken down leading to the release of free galactose into the juice. Clarification aids, in contrast, only caused a slight increase in free galactose concentrations due to its selective action on soluble pectin. Information gained from this project will allow dietitians to better manage the diet and cooking practices of galactosemic patients to reduce intake of galactose and alleviate the occurrence of complications.

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