High-temperature Short-time Process Research Articles

The inactivation and regeneration of peroxidase in relation to the high temperature–short time processing of vegetables

SummaryAs a result of the high thermal stability of peroxidase and its association with quality deterioration in high temperature–short time processed foods it was decided to investigate some aspects of the kinetics of inactivation of two purified grades of horseradish peroxidase.The following main conclusions were drawn:(a) It was shown that regeneration of peroxidase activity took place after partial inactivation at either 70, 90 or 110°C and that the first order plots of regenerated activity were biphasic in each case. Both fast and slow rates of regeneration increased on increasing the holding temperature from 30 to 40°C but no regeneration at all was observed at a temperature of 50°C. It was found that holding for 24 hr at 50°C almost completely prevented regeneration of peroxidase activity on further cooling. The extent of regeneration was found to be governed by the length of time at the inactivation temperature and a maximum was found which coincided with the high rate period of inactivation.(b) The first order plots of peroxidase inactivation were biphasic. Although the different purities of peroxidase did not give significantly different D121.1°C and z values for the low rate of inactivation over the temperature range 70–160°C, the presence of either pea or green bean purée significantly reduced the D121.1°C and, in the case of pea purée, increased the z value. It was also shown that the proportion of relatively stable enzyme was much lower in the presence of bean purée than in the presence of pea purée at each temperature.

EFFECT OF PROCESSING ON NUTRIENT COMPOSITION AND TEXTURE OF PRUNES

ABSTRACT.Skin texture was influence by hydration procedure with the methods requiring the longest time at high temperatures producing the tenderest skin. The texture of freshly hydrated prunes continued to change during the first 6–15 weeks of storage. Hydration method had a pronounced effect on the nutrient composition and texture of prunes. No vitamin A loss occurred when prunes were hydrated by a high temperature short time process, compared to an 18% loss in the slower procedures. The skin of the prune contained more vitamin A and iron than the pulp.

Decomposition of Organic Acids During Processing and Storage

Solutions (0.1 N) of organic acids as well as tissue concentration levels were processed at several temperatures with varyious F0 values. Analyses were done using an automatic organic acid analyzer and paper chromatography. Pyrrolidone-carboxylic acid was produced from glutamic acid, fumaric from maleic acid, itaconic and trans-aconitic from cis-aconitic acid, malonic acid decomposed to acetic acid, and oxalacetic to pyruvic acid. At tissue concentration level oxalacetic acid decomposed completely at all process temperatures to pyruvic acid and to a lesser degree during storage without processing. Decomposition of other organic acids increased with increasing process time. The decompositon of malonic to acetic acid was the only reaction which was decreased significantly by use of a High-temperature Short-time process. However, the amount of decomposition of all acids, except oxalacetic, was low both after processing and during storage.

Flavor of Evaporated Milk. II. Changes in Flavor on Storage of Evaporated Milk Made by Three Processes

The flavor stability of evaporated milk made by the conventional, high-temperature short-time, and aseptic processes was determined on storage at 10 and 27C. There was a significant effect of processing on the initial flavor score and on the effect of storage on the product at the two storage temperatures. The aseptic process yielded the best-flavored product initially and it remained the best for about two months at 10 and 27C storage. After two months the aseptic process showed very little advantage over the high-temperature short-time process. Evaporated milk made by the conventional process had the poorest flavor initially and throughout storage.