Chaim H. Mannheim

Dehydration of carrots by a combination of freeze drying, microwave heating and air or vacuum drying

Abstract Carrot slices were dried by combining freeze drying with a short microwave treatment and air or vacuum drying. Total drying time, and quality parameters including color, dimensions of slices and rehydration ratio were determined. Freeze drying for 2 h at a plate temperature of 30 °C followed by 1.5 h at 55 °C was sufficient to remove all water by sublimation and reach a product moisture of about 40%. The partially freeze dried product was microwave treated for 50 s and then dried to 5% moisture in vacuum or forced air. The color, dimensions and rehydration ratio of the partially freeze dried, microwave treated and air dried product were similar to same quality parameters of the product freeze dried to the final moisture content. Final drying in vacuum oven had some beneficial effect on color. A considerable saving in freeze drying time was achieved by combining freeze drying with microwave treatment followed by air drying. Total freeze drying time at 30 °C was 9.5 h as compared to a combination of 3.5–3.75 h of partial freeze drying followed by a short microwave treatment and 3.75 h air drying.

Internal corrosion and shelf‐life of food cans and methods of evaluation

Internal corrosion in food cans is characterized by metallic dissolution which is an electrochemical reaction. In lacquered cans, corrosion may also cause disruption in the continuity of the lacquer film. These reactions may cause organoleptic changes in the product, loss of vacuum, swelling, and leaking in extreme cases. In some instances the metal dissolution (i.e., lead) may give rise to toxicological problems. Therefore, these phenomena are often the limiting factor in the shelf life of canned products. Changes in color, texture, and sensoric properties of the foods, which take place simultaneously, affect the aesthetic and nutritional value of the product and thus its shelf life. These changes are often related to interactions with the container. For example, tin dissolution prevents browning and loss of ascorbic acid. Shelf life of canned foods is governed by the quality of the raw materials, the processing technology, quality of the container and storage conditions which will be reviewed in this paper. Can manufacturing technologies, mechanisms of electrochemical corrosion, methods of their measurement and prediction of shelf life will be discussed.

Heat penetration and quality preservation during thermal treatment in plastic trays and metal cans

Abstract A Comparative study of the rate of heat penetration and quality preservation during thermal processing and short term storage in high barrier plastic trays and comparable metal cans was carried out using a model system of bentonite suspension and ascorbic acid. The rates of heat penetration (fh, values) were 32 min for the trays and 52 min for the cans. The ascorbic acid retention, after thermal treatment to an Fo value of 11–12 min, was 83% for the trays and 75% for the cans. During storage, the rate of ascorbic acid degradation was similar in both packages. Therefore, after 107 days at 35 °C, the residual ascorbic acid in the trays remained still higher than that in the cans.

Control of water in foods during storage

Moisture content and its water activity (aw) are critical parameters affecting the shelf life of most food products. In most cases excessive amounts of water will cause spoilage, while in other cases loss of water will render foods unacceptable. The control of water in foods requires knowledge of their sorption/desorption behavior, critical moisture content, the environmental storage conditions of temperature and relative humidity, packaging parameters including volume to area ratios and permeability. Fast and reliable methods of evaluating the above parameters are needed to predict the storage life of foods. The importance of moisture control in produce as well as in dry products is discussed. Fast methods to evaluate water sorption/desorption behavior of foods are described. A computer program, which integrates all parameters required to predict the water dependent shelf life of foods, including changing conditions during storage, is also reported.

The dehydration, shelf-life and potential uses of citrus pulps

Abstract Technological treatments and drying conditions for citrus pulp, which accounts for 10–20% of the refuse from citrus juice plants, were established. Washed and unwashed pulp with 5 and 15% total solids (respectively) and partly washed material containing peel, with about 10% solids, served as raw materials. The flakes obtained from a drum drier (at about 4% moisture content) were non-uniform and had low bulk density. Water holding capacity was up to ten times their weight. Drying ratios of 7:1 and 18:1 depending on the total solid content of the raw material, and drying rates of 15–22 kg h −1 m −2 dry material were obtained on a pilot double drum drier. Antioxidants added prior to drying prevented fading and development of rancidity during storage. The drum dried product, kept in darkness, at temperatures below 25°C, maintained good colour, flavour and flowability for over a year. Substituting some of the flour, in Snap cookies and yeast cake, with citrus fibres showed they could serve as binding and filling agents. Sensory evaluation of these products showed those with levels up to 7·5% fibres (containing peel) and 20% fibres (without peel) were tasty.

Evaluation of Interaction of Lacquer Coated Cans with Melon Cubes by Electrochemical and Other Methods

AbstractElectrochemical measurements, visual appearance and estimation of dissolved iron were applied in order to assess the performance of lacquered tinplate cans filled with melon cubes and stored at 15,25,35 and 45°c. Visual appearance rating was found to relate well with polarisation resistance, indicating for a heavily attacked can a low visual score and a low resistance value. Corrosion potential values of the lacquered cans changed little with change in storage time and temperature, apparently due to the small dissolved metal concentration in this product. Corrosion currents, as obtained from potentiodynamic measurements, were found to increase linearly with time, and Q10 values of about 1·8 were calculated for the metal exposure rate. An equation relating current density with time and temperature, which enables the prediction of shelflife of the food-lacquered can system, was found. Corrosion currents obtained from linear polarisation and potentiodynamic measurements were found to be related, indi...

Environmental Problems in Food Production, Processing and Preservation

The extended use of fertilizers, herbicides, insecticides, etc., has increased crop yields, prevented losses and enabled the provision of a sufficient food supply for the “exploding population” on the one hand, but created serious problems on the other hand. These problems include: undesirable compounds in raw materials; additives used in processing and preservation which may have adverse effects; pollution from processing plants; disposal of food packaging. While much attention has been given to the intentional additives or residues from agro-technological treatments, much less attention has been paid to the potentially harmful compounds which occur naturally in plants used as foods.

Seasonal and Processing Influences on Bacterial Count of Raw and Processed Milk

An increase in total counts of raw milk was detected during summer in comparison to winter. The higher summer temperature did not affect the numbers of coliforms and staphylococci. The microbial contamination of pasteurized milk did not change significantly during the year. All bacterial counts increased during the flow of milk through the various systems of the dairy plant before the pasteurizer. It was shown that pipe lines could cause contamination of milk, especially at the beginning of flow after the line was temporarily shut down. A correlation between numbers of coliforms and staphylococci was found for both raw and pasteurized milk.

Measurement of stagnancy in a pipe line using a radioactive tracer and labelled bacteria

SummaryA stainless steel ‘T’ joint was used to simulate stagnant volume in a pipe-line. Residence time distribution in the lines was measured using a radiotracer (Cr51) which emitted γ radiation. The radiation was measured externally to the pipe line. From the experimental data the dead volume of the system was calculated. The effect of the depth of T and flow velocity on dead volume was evaluated. Labelled bacteria were used in some experiments instead of chromium. No significant difference in behavior between ionic chromium and bacteria labeled with chromium was found.