Keshavan Niranjan

Opportunities and Challenges in High Pressure Processing of Foods

Consumers increasingly demand convenience foods of the highest quality in terms of natural flavor and taste, and which are free from additives and preservatives. This demand has triggered the need for the development of a number of nonthermal approaches to food processing, of which high-pressure technology has proven to be very valuable. A number of recent publications have demonstrated novel and diverse uses of this technology. Its novel features, which include destruction of microorganisms at room temperature or lower, have made the technology commercially attractive. Enzymes and even spore forming bacteria can be inactivated by the application of pressure-thermal combinations, This review aims to identify the opportunities and challenges associated with this technology. In addition to discussing the effects of high pressure on food components, this review covers the combined effects of high pressure processing with: gamma irradiation, alternating current, ultrasound, and carbon dioxide or anti-microbial treatment. Further, the applications of this technology in various sectors—fruits and vegetables, dairy, and meat processing—have been dealt with extensively. The integration of high-pressure with other matured processing operations such as blanching, dehydration, osmotic dehydration, rehydration, frying, freezing / thawing and solid-liquid extraction has been shown to open up new processing options. The key challenges identified include: heat transfer problems and resulting non-uniformity in processing, obtaining reliable and reproducible data for process validation, lack of detailed knowledge about the interaction between high pressure, and a number of food constituents, packaging and statutory issues.

Recent developments in osmotic dehydration: methods to enhance mass transfer

Abstract Osmotic dehydration, due to its energy and quality related advantages, is gaining popularity as a complimentary processing step in the chain of integrated food processing. Generally, osmotic dehydration being a slow process, there has been a need for additional ways to increase the mass transfer without adversely affecting the quality. This gave the required motivation for many recent advances in this area. However, certain constraints still exist for the wide industrial adoption of osmotic dehydration, which need to be addressed in current and future research in the area. In order to compare the results of various investigators, there is a need to express research results in terms of more fundamental parameters like diffusion coefficient. Consequently, suitable methods to estimate such parameters in various foods of different size and geometry are discussed. The mechanism of osmotic dehydration proposed recently is described. Various methods to increase the rate of mass transfer, such as application of high hydrostatic pressure, high electrical field pulses, ultrasound, vacuum and centrifugal force are also presented.

Mass transfer during osmotic dehydration of banana: Fickian diffusion in cylindrical configuration

Abstract Mass transfer during osmotic dehydration of banana has been studied. The solution of Ficks law for unsteady state mass transfer in cylindrical configuration has been used to calculate the effective diffusion coefficients over a range of temperature (25–35 °C) and concentration (40–70 °B) of osmotic solution. The effective diffusion coefficient has been empirically correlated with the concentration and temperature of osmotic solution by an Arrhenius-type equation. A high degree of correlation ( R 2 = 0.97) was observed between predicted and experimental values of the effective diffusion coefficient.

Simultaneous Aqueous Extraction of Oil and Protein from Soybean: Mechanisms for Process Design

Aqueous extraction of oil and protein from soybean flour was investigated to elucidate the mechanisms involved. The process variables investigated were: particle size, temperature, time, pH, power input, solid-to-liquid ratio, use of several extraction steps, and the use of preliminary heat treatment prior to the extraction. Protein and oil extraction yields were shown to be closely related, both depending on the level of disruption of cell wall. Experimental investigations show that protein extraction from the disrupted cells follows a solubilization/diffusion mechanism. Conditions that favour protein extraction—i.e., temperature below the level causing denaturation, pH away from the isoelectric point, and use of several extraction steps—generally favour oil extraction. However, the mechanisms governing protein extraction rates are quite different from those governing oil extraction rates. The extraction mechanisms are also elucidated in the context of the cell structure, and the response to different extraction parameters form the basis for the process design and optimization.

Extraction of rice bran oil using aqueous media

Aqueous extraction of oil from rice bran was studied on a laboratory scale and the resulting product was examined. The following process parameters influencing oil extraction were individually investigated: pH of aqueous media, extraction temperature, extraction time, agitation speed and rice bran-to-water ratio. Extraction temperature and pH were found to be the main factors influencing oil extraction. The highest oil yield was obtained at pH 12.0, extraction temperature 50 °C, extraction time 30 min, agitation speed 1000 rpm, and rice bran-to-water ratio 1.5-to-10. The quality of aqueous-extracted oil in terms of free fatty acid, iodine value and saponification value was similar to a commercial sample of rice bran oil and hexane-extracted oil, but the peroxide value was higher. Furthermore, the colour of aqueous-extracted oil was paler than solvent-extracted oil. © 2000 Society of Chemical Industry

Pervaporative stripping of acetone, butanol and ethanol to improve ABE fermentation

Acetone-butanol-ethanol fermentation by anaerobic bacterium C. acetobutylicum is a potential source for feedstock chemicals. The problem of product induced inhibition makes this fermentation economically infeasible. Pervaporation is studied as an effective separation technique to remove the toxic inhibitory products. Various membranes like Styrene Butadiene Rubber (SBR), Ethylene Propylene Diene Rubber (EPDM), plain Poly Dimethyl Siloxane (PDMS) and silicalite filled PDMS were studied for the removal of acetone, butanol and ethanol, from binary aqueous mixtures and from a quaternary mixture. It was found that the overall performance of PDMS filled with 15% w/w of silicalite was the best for removal of butanol in binary mixture study. SBR performance was best for the quaternary mixture studied.

Recovery of Dissolved Essential Oils from Condensate Waters of Basil and Mentha arvensis Distillation

Adsorptive recovery of perfumery components from steam distillation condensates of basil and Mentha arvensis has been studied. Initially, the steam distillation condensates were analysed for the aroma components present. Amberlite XAD-4 was used as the adsorbent. Ethanol was used as the eluent. For both the cases, a recovery of greater than 90% was obtained.

Effect of thermal processing on available lysine, thiamine and riboflavin content in soymilk

Soymilk was heated over a range of temperatures (90–140°C) and times (0–6 h). The available lysine, thiamine and riboflavin content of the soymilk samples were determined. There was no significant change in available lysine during a 3 h heating period at 95°C. At elevated temperatures of 120 and 140°C, optimum heat processed soymilk gave higher measured values of available lysine than did soymilk processed at 95°C. Prolonged heating at 120 and 140°C caused a decline in available lysine. Kinetic data on the thermal degradation of thiamine and riboflavin in soymilk were fitted with first-order kinetics and the kinetic parameters were determined.

The potential to intensify sulforaphane formation in cooked broccoli (Brassica oleracea var. italica) using mustard seeds (Sinapis alba)

Sulforaphane, a naturally occurring cancer chemopreventive, is the hydrolysis product of glucoraphanin, the main glucosinolate in broccoli. The hydrolysis requires myrosinase isoenzyme to be present in sufficient activity; however, processing leads to its denaturation and hence reduced hydrolysis. In this study, the effect of adding mustard seeds, which contain a more resilient isoform of myrosinase, to processed broccoli was investigated with a view to intensify the formation of sulforaphane. Thermal inactivation of myrosinase from both broccoli and mustard seeds was studied. Thermal degradation of broccoli glucoraphanin was investigated in addition to the effects of thermal processing on the formation of sulforaphane and sulforaphane nitrile. Limited thermal degradation of glucoraphanin (less than 12%) was observed when broccoli was placed in vacuum sealed bag (sous vide) and cooked in a water bath at 100°C for 8 and 12 min. Boiling broccoli in water prevented the formation of any significant levels of sulforaphane due to inactivated myrosinase. However, addition of powdered mustard seeds to the heat processed broccoli significantly increased the formation of sulforaphane.

Why use bubble-column bioreactors?

Abstract Among the plethora of bioreactors available for aerobic culture, bubble columns, which are composed of a cylindrical vessel fitted with a gas sparger, are gaining in use. The simple construction of bubble-column reactors makes them easy to maintain. In addition, it is possible to control the degree of shear, uniformly within the reactor, which is critical to the growth of plant and animal cells in particular. This article reviews in detail the hydrodynamic, heat and mass-transfer characteristics of bubble-column bioreactors - parameters that are important for industrial scale-up.