Food and nutrition.pdf

266 . Food Spoilagethe action of enzymes. This g~neral definition includes virtually allchemical reactions of physiological importance, and scientists today oftenrestrict the term to the action of specific enzymes, called ferments,produced by minute organisms such as molds, bacteria, and yeasts. Forexample, 'lactase, a ferment produced by bacteria usually found in milk,causes the milk to sour by changing lactose (milk sugar) into lactic acid.Formula of fermentation:carbohydrate foods + saccharolytic microorganismsJ,acids + alcohol + gases(carbon dioxide)RancidityMicrobial RancidityLike all food components, fats undergo deteriorative changes withtime, which result in undesirable flavors and odors. These changes in fatsare given the term "rancidity".Formula of microbial rancidity:fatty foods + lipolytic microorganismsJ,fatty acids + glycerolHydrolytic RancidityFatty acids formed through hydrolysis of the lipid(fat) by the waterwhich it contains. Some of the liberated fatty acids are volatile, and somehave very unpleasant odours and flavours. Formula of hydrolytic rancidityoCH o-l-c H CHpH 02 0 17 35 II 1/ 1/CHO-C-C H (5) + H O{l)-C,!i35 C0 2 H(aq) + CHO-C Ō C17 H 35 (I)0 17 35 2 II 1/ 1/CH O-C-C HCHP-C-C,!i352 17 35Trioctadecanoylglycerol + Water-Octandecanoic acid + Dioctadecanoylglycerol(tristearin) (stearic acid) (disterin)Oxidative RancidityThe oxidation of acylglycerols which occurs in air, without thepresence of enzymes, is called autoxidation. Among the products ofautoxidation are hydroperoxides, ROOH. These have no taste, but theydecompose easily to form aldehydes, ketones and acids, which giveoxidised fats and oils their rancic~ flavours. It can be slow down by addition. of antioxidants.