K.S.M.S. Raghavarao

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.

Developments in Osmotic Dehydration

Publisher Summary Osmotic dehydration can be considered as the most eligible energy-saving method for the partial removal of water from foods, if and even as a method of preservation in case of candy preparation. It can affect marked reduction in the moisture content of the foods before they are subjected to further processing steps such as drying, freezing, or frying. Pretreatment with osmotic solution having concentrations lower than the natural cell concentration can improve rehydration characteristics. Osmotic dehydration can also be used for the natural concentration of fruits, which helps in obtaining better characteristics of food prepared from them, such as jam. Application of various pretreatments to osmotic dehydration such as high hydrostatic pressure, high electrical field pulses, gamma irradiation, ultrasound, vacuum, and centrifugal force, can overcome the long existing issues related to the inherently slower mass transfer rates. With the advent of newer technologies involving adsorbence and membranes, the problem of handling used osmotic solution may find newer means of resolution, which will further increase the economical feasibility of this technology.

Mass Transfer During Osmotic Dehydration: Determination of Moisture and Solute Diffusion Coefficients from Concentration Profiles

Mass transfer during osmotic dehydration was studied. The effective diffusion coefficients for water and solute diffusion were determined assuming osmotic dehydration to be governed by Fickian diffusion. Solution of Ficks law for unsteady-state mass transfer was used to estimate the effective diffusion coefficients. The average effective diffusion coefficients (D e ) obtained by this method could predict the moisture ( r 2 =0.95) and solid (( r 2 =0.96) content to a sufficient accuracy. A high degree of correlation was observed between predicted and experimental values of moisture and solid content.

Removal of toxic Congo red dye from water employing low-cost coconut residual fiber

The coconut residual fiber (CRF) is the major byproduct obtained during production of virgin coconut oil. Its application as a biosorbent for adsorption of Congo red was investigated. The CRF was subjected to different pretreatments, namely, pressure cooking, hexane treatment, acid treatment and their combinations. The pretreatment of CRF with the combination of hexane, acid, and pressure cooking resulted in the highest degree of adsorption. The equilibrium data were analyzed and found to fit best to both Langmuir and Freundlich isotherms. Thermodynamic parameters such as standard free energy (ΔG0 kJ mol-1), standard enthalpy (ΔH0, kJ mol-1) and standard entropy (ΔS0, kJ mol-1 K-1) of the systems were calculated by using the Langmuir constant. The ΔG0, ΔH0 and ΔS0 were found to be 16.51 kJ mol-1, -19.39 kJ mol-1 and -0.12 kJ mol-1 K-1, respectively, at 300 K. These thermodynamic parameters suggest the present adsorption process to be non-spontaneous and exothermic. The adsorption process was observed to follow pseudo-second-order kinetics. The results suggest that CRF has potential to be a biosorbent for the removal of hazardous material (Congo red dye) with a maximum adsorption capacity of 128.94 mg g-1 at 300 K.

Recent Developments in Osmotic Dehydration

Osmotic dehydration can be considered as the most eligible energy saving method for the partial removal of water from foods, if and even as a method of preservation in the case of candy preparation. It can affect marked reduction in the moisture content of the foods before they are subjected to further processing steps such as drying, freezing, frying, etc. The pretreatment with the osmotic solution having concentrations lower than the natural cell concentration can improve the rehydration characteristics. Osmotic dehydration can be used also for the natural concentration of fruits, which helps in obtaining better characteristics of food prepared from the same, such as jam. The application of various pretreatments to osmotic dehydration such as application of high hydrostatic pressure, high electrical field pulses, gamma irradiation, ultrasound, and vacuum and centrifugal force, can overcome the long-existing issues related to inherently slower mass transfer rates. The basic understanding of the mechanism of mass transfer during osmotic dehydration will play an important role in devising novel applications of this potential technique in food processing by future researchers.

Athermal Membrane Processes for the Concentration of Liquid Foods and Natural Colours

Abstract Liquid foods (fruit juices and natural colors) are gaining importance in the food industry because they contain components beneficial for human health. Both fruit juices and natural colors, when extracted from their sources, have a low solid content, color strength, and a high water load. Water, being the major constituent of liquid foods/natural colors, contributes to the growth of microorganisms. Concentrating liquid foods provides a reduction in transport, packaging, and storage costs. The juice industry has developed a complex recovery of essence, careful process control, and blending techniques to produce a good quality concentrate that is acceptable to consumers. However, it is still easily distinguishable from fresh juice. Natural colors are heat sensitive (they show changes in color intensity), hence it is necessary to concentrate dilute solutions using methods that operate at ambient temperature. Many efforts have been reported regarding improved methods such as freeze concentration, sublimation concentration, and concentration by using membranes such as ultrafiltration, nanofiltration, and reverse osmosis for the concentration of liquid foods (fruit juices and colors). The most promising alternative is membrane-based concentration, which does not involve any heat or pressure driven processes, as do osmotic membrane distillation or direct osmosis. The merits and demerits of these membrane processes, along with the possibilities for integrating them with existing processes are discussed in this chapter.

Storage study and quality evaluation of coconut protein powder.

Coconut skim milk and insoluble protein are 2 major byproducts in the production of virgin coconut oil. Coconut skim milk was homogenized along with insoluble protein and spray dried to obtain a value-added product, namely, coconut protein powder (CPP). This study deals with the storage study of CPP under different conditions (refrigerated [control], ambient and accelerated). CPP samples were withdrawn periodically at designated intervals of 15 d for accelerated and control, and 30 d for ambient condition. CPP stored at different conditions exhibited marginal moisture uptake (by 0.74 % w/w for control, 0.76 % w/w for ambient, and 1.26 % w/w for accelerated condition) and as a result, had very little effect on the functional properties of the powder. Withdrawn CPP was tested for sensory quality aspects and subjected to instrumental analysis as well. Withdrawn CPP was incorporated as a milk substitute in dessert (Kheer). Quantitative descriptive analysis of the powder and product (Kheer) showed no significant difference in attributes of CPP during the storage period of 2 mo. Electronic nose analysis revealed that CPP samples were not much different with respect to aroma pattern matching, respectively.

Acoustic field assisted demixing of aqueous two-phase polymer systems

Acoustic field assisted demixing was employed to decrease the demixing time in polymer–polymer (polyethylene glycol–maltodextrin) two-phase system. Application of acoustic field has decreased the demixing time in these systems up to 2-fold. Ultrasonication has induced mild circulation currents in the phase dispersion, which has enhanced the rate of droplet coalescence, eventually resulting in decreased demixing time. In polymer-polymer systems, phase demixing was found to depend greatly on which of the phases is continuous and viscosity of the continuous phase was observed to have a strong influence on the movement of the droplets and hence the phase demixing. Addition of NaCl increased the demixing time and presence of E.coli cells did not seem to have any influence on phase demixing.