Quality of home frozen vegetables

Summary The previous paper in this series covered organoleptic and Vitamin C assessments of vegetables blanched and/or cooled in various salt and sugar solutions, and stored at – 18°C for up to 12 months. This paper deals with the effects of these additives on percentage conversion of chlorophyll to phaeophytin after blanching or after storage. Dietrich's method (1958) was used for the assays. Results indicated that a number of salts (NaCl, KCl, Na2SO4, K2SO4) added to blanching water had little effect on pH, but could cause a considerable reduction in the amount of chlorophyll conversion in spinach and sprouts. Levels of NaCl above 1·2% in tap blanching water and the addition of 1·2% NaCl to the cooling water were less effective than the addition of 1·2% salt to the blanching water. During serial blanching in 1·2% NaCl tap water, chlorophyll retention was highest after the first blanch. In peas and runner beans 1·2% NaCl added to tap blanching water caused little reduction in chlorophyll conversion, but during 9 months storage the beneficial effect of the salt was maintained in the uncooked material. 0·25% sodium carbonate had the greatest effect in increasing pH and in reducing chlorophyll conversion. 0·25% sodium bicarbonate reduced conversion to the same extent as 1·2% NaCl, but induced an increase in pH. Using distilled water, levels of conversion were much higher, and the 1·2% NaCl treatments had a greater effect. Sucrose was not effective in preventing conversion.