High-temperature Short-time Process Research Articles

UHT Milk Processing—Effect on Process Energy Requirements

ABSTRACTEnergy requirements for processing milk using a free falling film steam infusion ultra‐high temperature (UHT) sterilization process and a high temperature‐short time (HTST) pasteurization process were determined and compared. Product flow rate was 2500 kg/hr. Milk to milk regeneration was used with both processes. UHT process temperatures were 138, 143, 149, and 154°C. The energy requirements for the UHT and HTST processes ranged between 573 and 667 kJ/kg milk and 217 and 228 kJ/kg milk, respectively. Although the UHT process consumed between 345 and 450 W/kg milk additional energy in the plant, the UHT sterilization of milk has been estimated to result in a net energy savings of 547 ‐ 652 kJ/kg milk because the product does not require post‐processing refrigeration.

CONCENTRATION OF WATERMELON JUICE

ABSTRACTA high temperature short time process was used to produce a 65° Brix concentrate from watermelon juice. Color of the reconstituted juice was similar to color of the fresh juice. The concentrate could be stored at ‐21°C for 18 months without color loss. The dominant pigment in the concentrate is lycopene and it could be extracted in a relatively pure form. Watermelon concentrate showed a psuedoplatic behavior with apparent viscosities lower than orange and grapefruit juice concentrates within the shear rates of 2‐100 set‐1.

Development of quick‐cooking dehydrated pulses by high temperature short time pneumatic drying

SummaryQuick‐cooking dehydrated pulses were made from husked split grains of red gram, black gram and Bengal gram using high temperature short time (HTST) pneumatic drying technique wherein porosity was brought about in the dried pulses by exposure of the cooked grains initially to air at a high temperature (170–200°C) for a short duration (4–6 min) in a laboratory model HTST pneumatic drier followed by finish drying at a lower temperature (60–70°C) in a conventional tray or fluidized bed drier. Optimum temperature and time for the HTST drying of the grains were worked out and the HTST dried products were evaluated with respect to their drying behaviour, rehydration characteristics and shelf stability vis‐a‐vis the conventional hot air dried products.Considerable reduction in drying and rehydration times could be achieved by the HTST process. The increase in porosity achieved and the HTST treatment did not adversely affect the shelf stability of the grains to any measurable extent.The technique involves simple equipment and less capital investment as compared to other methods of drying, such as explosive puffing, achieving the same objective. It is amenable to continuous processing as the time of high temperature drying is very short.

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.