H. Umesh Hebbar

Mass transfer during infrared drying of cashew kernel

The aims of this study were to determine the effects of temp. on infrared drying of cashew nuts and investigate mass transfer during this process. Cashew nuts with intact testa layer were dried in an infrared oven (far infrared source, 3-15 mum) at 100, 110 and 120C and moisture content was determined at different time intervals within the range 2.5-30 min. Moisture diffusion coeff. were estimated using a modified solution of Ficks unsteady state diffusion equation; cashew nuts were considered to have spherical configuration in the model. The Arrhenius equation was used to describe the dependence of effective diffusion coeff. on infrared drying temp. The proposed model provided accurate prediction of moisture content of cashew nuts at any given time during the drying process. An activation energy value of 28.7 kJ/mol was calculated for infrared drying of cashew nuts.

Processing of Honey: A Review

Thermal processing of honey eliminates the microorganisms responsible for spoilage. Microwave heating, infrared heating, ultrasound processing, and membrane processing have been explored as alternatives to conventional heat processing. Microwave heating provides a rapid method for achieving the desired level of yeast reduction with reduced thermal damage. Infrared heating is not as rapid as microwave heating but desired results are achieved in a relatively shorter duration (3 to 4 minutes) compared to the conventional method. Membrane processing is an athermal process and very effective in the complete removal of yeast cells from honey. Microfiltration and ultrafiltration could be employed to produce enzyme-enriched honey besides clarified honey.

Processing of honey using polymeric microfiltration and ultrafiltration membranes

Rejection of enzymes and elimination of yeast cells from honeys, using various mol. wt. cut off (MWCO) membranes, were examined in the clarification procedure. Use of membrane technology to produce a honey which is free from microorganisms and suspended matter, but which contains a significant level of enzymes, was also evaluated. Forest/Rock bee honey (Apis dorsata) was strained through a muslin and used in the experiments. Honey samples were analysed for diastase activity, sugars, yeast counts and hydroxymethylfurfural (HMF) value. Permeates from membranes with MWCO of 25-100 (x 103) exhibited no diastase activity; permeate flux rates were 0.9-1.15 kg m-2 h-1. Membrane processing completely removed yeasts. A microfiltration membrane of pore size 100 nm eliminated microorganisms whilst retaining nutritional factors; an ultrafiltration membrane of 20 000 MWCO fractionated this microfiltered honey into 2 fractions, i.e. an enzyme-rich honey (enzymes enriched 2.2x) and a regular ultrafiltered honey. Because honey is viscous, it required dilution before membrane processing, so subsequent vacuum concn was evaluated; as processing temp. increased, HMF value and loss of enzymes increased; it is thus suggested that this process should be conducted at as low a temp. as possible.

Acoustic field-assisted osmotic membrane distillation

Abstract Osmotic membrane distillation (OMD) is a novel membrane process that facilitates the concentration of aqueous solutions under mild operating conditions. The main drawback of OMD, like any other membrane process, is relatively low flux. In the present work acoustic field has been applied for the enhancement of transmembrane flux. Acoustic field, using transducer, of the frequency 1.2 MHz was applied perpendicularly to the membrane. Encouraged by the initial results of reasonable enhancement in the transmembrane flux (by 20–30%), further experiments were carried out for 5 M NaCl/pure water, 5 M CaCl2/pure water, NaCl/sugarcane juice and CaCl2/sugarcane juice systems both in the presence and absence of acoustic field. It was observed that there was about 22–205% enhancement in transmembrane flux with the application of acoustic field. All the experiments have been carried out in a membrane cell using different hydrophobic membranes polytetrafluoroethylene and polypropylene). The effect of various parameters such as concentration (2, 3, 4, 5 M), stirring speed (0, 198, 250, 450 rpm) and temperature (40, 50, 60°C) was studied on transmembrane flux in the absence of acoustic field, and the effect of acoustic field was studied at the best conditions observed. PTFE and PP membrane fluxes for CaCl2 were both higher in the case of sugarcane juice and water than those for NaCl and K2HPO4 solutions. Results obtained from these experiments were correlated using a modified Nernst film model.

Properties of Dried and Intermediate Moisture Honey Products: A Review

This review discusses the processing techniques proposed for the production of dried and intermediate moisture honey products, as well as their properties. Stickiness is the major problem in the drying of sugar rich products like honey, that depend on the type of sugar and temperature of operation, which are related to the glass transition temperature. Some additives are usually added to the sugary feed to increase the glass transition temperature and concurrently the sticky point temperature. In the case of honey-fruit spreads, nutritional and sensory characteristics can be enhanced by replacing part of sugar with honey. Co-crystallization of honey with sucrose could be used to preserve the honey flavor. These diversified honey products provide better taste and nutrition to the consumer besides enhancing the utilization of honey.

Effect of drying methods on the quality characteristics of dill (Anethum graveolens) greens.

Different drying methods hot air (HA), 50 °C, 58-63% relative humidity (RH); low humidity air (LHA), 50 °C and 28-30% RH; and radiofrequency (RF), 50 °C, 56-60% RH) were investigated for efficient dehydration of dill (Anethum graveolens) greens with optimal retention of color and constituents. The drying for HA and RF was marginally higher (∼ 22%) compared to HA. Lightness, greenness and yellowness of LHA dried sample were higher than those of the RF and hot-air dried dill greens. Aqueous methanolic extract of dill greens dehydrated by LHA method exhibited higher anti-oxidant activity. Forty-two compounds were identified representing ∼ 85% of the volatile oil and the major volatile compounds for fresh and dried dill leaf oil were α-Phellandrene, α-cymene, α-pinene, Apiol, 1,6-Cyclodecodiene, and 1-methyl-5-methylene. Dehydrated dill greens with their constituent polyphenols, carotenoids, ascorbic acid and minerals have been shown good consumer acceptance as well as shelf life and could serve as a valuable food additive to enhance human nutrition.

Reverse Micellar Extraction of Bromelain from Pineapple (Ananas comosus L. Merryl) Waste: Scale-up, Reverse Micelles Characterization and Mass Transfer Studies

Scale-up studies for phase transfer mode of reverse micellar extraction are attempted for the separation and primary purification of bromelain (EC 3.4.22.33) from pineapple (Ananas comosus L. Merryl) waste. Characterization of reverse micelles and mass transfer studies for the real system has been attempted for the first time. Scale-up of the extraction process employing commercial grade surfactant cetyltrimethylammonium bromide (CTAB) and solvent isooctane resulted in purification of 2.43 fold with an activity recovery 81.3%. The reverse micellar size estimated using empirical and geometrical models indicated that the reverse micelles are large enough (Rm = 7.2–9.6 nm) to host bromelain molecules that are relatively smaller in size (∼1.67 nm). The studies on the kinetics of mass transfer indicated a relatively slower rate (by ∼34%) of mass transfer in case of back extraction compared to forward extraction. Process scale-up did not significantly affect the extraction efficiency whereas purity of phase components played a major role. The mass transfer across the phases was high in the initial period of mixing for both forward and back extractions.

Recent Developments in Superheated Steam Processing of Foods—A Review

Although the use of superheated steam has been known for quite a long time, only in the recent past has it emerged as a viable technology for food processing. Superheated steam, having higher enthalpy, can quickly transfer heat to the material being processed, resulting in its rapid heating. The major advantages of using superheated steam for food processing are better product quality (color, shrinkage, and rehydration characteristics), reduced oxidation losses, and higher energy efficiency. This review provides a comprehensive overview of recent studies on the application of superheated steam for food-processing operations such as drying, decontamination and microbial load reduction, parboiling, and enzyme inactivation. The review encompasses aspects such as the effect of superheated steam processing on product quality, mathematical models reported for superheated steam drying, and the future scope of application in food processing. Recent studies on process improvisation, wherein superheated steam is used at low pressure, in fluidized bed mode, sequential processing with hot air/infrared, and in combination with micro droplets of water have also been discussed.

Effect of Additives on Quality of Spray-Dried Fructooligosaccharide Powder

Fructooligosaccharide (FOS) finds its applications as an alternative sweetener in powder form. The effect of different process parameters (feed concentration, feed flow rate, inlet air temperature), different additives (maltodextrin, gums, starch), and anticaking agents (in different combinations and concentrations) during spray drying were investigated. FOS solution with 2% magnesium oxide as an additive gave a maximum powder yield (43% w/w), and the spray-dried powder size was fine and the texture was like talcum powder. Flow properties and microbial analysis were found to be satisfactory. The addition of anticaking agents did not have a significant effect either on the color of the powder or on FOS content, indicating good quality of the powder with respect to flowability, microbial load, and texture.

Microwave Heating of Fluid Foods

Publisher Summary Food preservation is the primary objective of most food-processing operations and the challenge is to ensure quality and safety of processed products. Dielectric heating, which utilizes electromagnetic radiations such as microwave (MW) and radiofrequency (RF), is gaining popularity in food processing. Among them, MW has shown a great potential to be used as an alternative to conventional heating. These novel processing technologies are regarded as volumetric forms of heating, wherein the heat is generated from inside, as compared to surface heating with conductive or convective modes of heating. The volumetric heating of materials leads to higher rates of heat and mass transfer, resulting in reduced processing times and uniform product quality. Increasing demand for high-quality foods as well as cost competitiveness has necessitated the application of employing electromagnetic radiation, namely, MW-based processes for thermal processing. The efficiency of MW processing depends on many factors, which are broadly classified as system parameters and product parameters. Dielectric properties of foods, one of the important product parameters, are influenced by many factors, such as MW frequency, temperature, moisture content, and other food compositions. MWs have found applications in the areas of pasteurization, blanching, thawing, and concentration for liquid foods such as milk, fruit juice, puree, and pulp. Dehydration, roasting, cooking, tempering, baking, and extraction are some of the other applications of MW in food processing. Hybrid drying techniques wherein MW is combined with other processes have been reported to be highly efficient as compared to processing with MWs alone.