Quality of home frozen vegetables

Abstract

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 (NaC1, KC1, Na,SO,, K,SO,) added to blanching water had little effect on pH, but could cause a considerable reduction in the amount of chlorophyll conversion ip spinach and sprouts. Levels of NaCl above 1.2% in tap blanching water abd the addition of 1.2% NaCl to the cooling water were less effective thah 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. I n 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 p H and in reducing chlorophyll conversion. 0.25% sodium bicarbonate reduced conversion to the same extent as 1.2% NaC1, 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.

Quality of home frozen vegetables.

“…Addition of salt does not affect pH and it is thus probable that the salt blanch prevents leaching of the magnesium ions during blanching and cooking. Higher levels (3%) of salt may have an even greater protective effect in soft water areas (Hudson et al, 1974a). The results indicate that although 1.2% salt may help to prevent chlorophyll conversion, it cannot entirely prevent chlorophyll loss in acidic media.…”

“…Salt blanches tended to decrease loss of total chlorophyll during scalding, but only with soft water samples was the difference significant (P = 0.01). Again (Hudson et al, 1974a) there was no advantage in adding 3% salt to the cooling water, indicating that salt is ineffective in cold water.…”

Quality changes in frozen Brussels sprouts during storage. II. Objective quality parameters: texture, colour, ascorbic acid content and microbiological growth

“…It is long since known that conversion of chlorophyll to pheophytin takes place in vegetables during frozen storage (Dietrich et al, 1957;Dietrich et al, 1959;Dietrich, Huxsoll & Guadagni, 1970;Eheart & Odland, 1973;Walker, 1964;Hudson, Sharples & Gregory, 1974) and sterilization (Gold & Weckel, 1959). It is also known that this conversion can be measured as a change in sensorical appearance (Walker, 1964) and physical colour (Dietrich et al, 1957;Dietrich et al, 1959;Gold & Weckel, 1959).…”