Shanker Lal Shrivastava

Onion dehydration: a review

Onion (Allium cepa), a very commonly used vegetable, ranks third in the world production of major vegetables. Apart from imparting a delicious taste and flavour due to its pungency in many culinary preparations, it serves several medicinal purposes also. Processing and preservation of onion by suitable means is a major thrust area since a long time. The various kinds of treatments followed for dehydration of onion such as convective air drying, solar drying, fluidized bed drying, vacuum microwave drying, infrared drying and osmotic drying are reviewed here. These techniques are mainly used for preservation and value addition of onion. Several researchers have tried for decades to model the drying kinetics and quality parameters, which are also compiled here briefly.

Characterization of vacuum dried onion slices

Assessment of various quality parameters of vacuum dried onion, with or without pretreatment was attempted. Colour, flavor and rehydration ratio were analyzed and compared with those of convective air drying. Tissue microstructure images of dehydrated onion were studied and compared with convective air drying and microwave drying, with the help of scanning electron microscopy. The texture of dried onion was measured in terms of hardness, cohesiveness, springiness, gumminess and chewiness using texture analyzer. All these parameters were higher in case of treated samples compared to untreated ones. True density and thermal conductivity of vacuum dried onion were assessed with the changing moisture content. Colour, flavor and microstructure of vacuum dried onion were better than convective air drying. True density was found less compared to hot air dried product however thermal conductivity was almost comparable. The vacuum drying method for onion was found suitable over convective air drying which is normally practiced commercially.

Non-enzymatic browning and flavour kinetics of vacuum dried onion slices

Abstract Onion slices were dehydrated under vacuum to produce good quality dried ready-to-use onion slices. Colour development due to non-enzymatic browning and flavour loss in terms of thiosulphinate concentration was determined, along with moisture content and rehydration ratio. Kinetics of non-enzymatic browning and thiosulphinate loss during drying was analysed. Colour change due to non-enzymatic browning was found to be much lower in the case of vacuum dried onion, and improved flavour retention was observed as compared to hot air dried onion slices. The optical index values for non-enzymatic browning varied from 18.41 to 38.68 for untreated onion slices and from 16.73 to 36.51 for treated slices, whereas thiosulphinate concentration in the case of untreated onion slices was within the range of 2.96-3.92 μmol g-1 for dried sample and 3.71-4.43 μmol g-1 for the treated onion slices. Rehydration ratio was also increased, which may be attributed to a better porous structure attained due to vacuum drying. The treatment applied was found very suitable in controlling non-enzymatic browning and flavour loss during drying, besides increasing rehydration ratio. Hence, high quality dried ready- to-use onion slices were prepared.

Moisture transfer modeling during solar drying of potato cylinders considering shrinkage

ABSTRACT In the present work, the thin layer drying kinetics of potato during natural convection solar drying was investigated experimentally. Cylindrical potato samples with length 50 mm and varying diameter of 8, 10 and 13 mm were dried in an in-house designed and fabricated laboratory scale mixed-mode solar dryer. Thirteen different thin-layer mathematical models were fitted to the experimental moisture ratio (MR) data. The obtained results indicated that the Modified Page model could satisfactorily describe the drying curve of potato cylinders with higher value of R2 and lower values of RMSE and χ2. The shrinkage parameter is incorporated in the analytical diffusion model to study the moisture transfer mechanism of potato cylinders. It was observed that the values of effective diffusion coefficient (Deff) and convective mass transfer coefficient (hm) are overestimated in the range of 85.02–90.27% and 39.11–45.11% for the range of sample diameter examined, without considering the shrinkage effect in the mass transfer analysis. A Multiphysics approach was adopted in this study to get insight into the drying behavior of potato cylinders in terms of food-moisture interactions during the solar drying process. The predicted results of MR are in close agreement with the experimental data. Moreover, the anisotropic behavior of shrinkage as well as the moisture distribution inside the potato cylinder was very well described by Multiphysics model.

Effect of pretreatment on rehydration, colour and nanoindentation properties of potato cylinders dried using a mixed-mode solar dryer

BACKGROUND Desirable quality estimation is an important consumer driver for wider acceptability of mixed-mode solar drying of potatoes in food industries. The aim of this study is to characterise rehydration, colour, texture, nanoindentaion and microstructure of dried potato samples and to establish the influence of pre-drying treatment on the above qualities. RESULTS The water absorption capacity and rehydration ability of solar dried potato were significantly influenced by pretreatment followed by rehydration temperature and sample diameter. The redness index (a*) of pretreated dried samples was lower with simultaneous higher value of yellowness index (b*), chroma (C*) and hue angle (h*). Also, the average nanohardness (H) of pretreated samples increased significantly by 22.64% compared to that of untreated samples. The average reduced modulus (Er ) and Youngs modulus (Es ) of dried potato samples were 1.865 GPa and 1.403 GPa, respectively. Moreover, creep displacement of 43.27 nm was traced in the untreated potato samples during a 20 s dwell time under a constant load of 200 µN in the nanoindentation test. Micrographs revealed more uniform pore spaces in pretreated samples. CONCLUSION Pretreated, thinner potato samples achieved better quality dried products in terms of rehydration, colour, texture and nanohardness indices with significantly improved microstructure and creep resistance properties.

Self-assembled carbohydrate nanostructures: synthesis strategies to functional application in food

Self-assembled carbohydrate nanostructures are drawing research attention due to high biocompatibility levels and potentiality to be used in several functional applications ranging from drug delivery to functional food. In this chapter efforts are made to provide an outline of the recent advancement of carbohydrate-based self-assembly strategies for food applications. A discussion of assembling strategies, behavior, and structure–function relationship associated with varying shapes and sizes is done to give broader direction to assembly strategy, its enhancement and control. Different self-assembly strategies with the food applications will help and appeal to people working in developing self-assembled functional biomaterials for food applications.

Economic Analysis of Cashew Nut Processing in India

Cashew (Anacardium occidentale) tree grows widely in warm and humid climatic regions of the world. India is leading producer and processor of cashew nuts. Cashew nut processing has undergone lot of developments from traditional to modern processing. Survey was done in various cashew nut processing units in different parts of West Bengal, and a case study is presented regarding economic analysis of a local small scale cashew nut processing plant of 100 kg capacity. Based on the observations, economic analysis of cashew nut processing plant showed that, if the plant be operated with full capacity and efficiency then there would be profit of 1329.07 per day, excluding all expenses. This is quite profitable, but the profit margin could be increased more by plant mechanization and modernization. Processing capacity could be increased with significant reduction in labour requirement and processing time by modernizing the processing plants.

Fungi Fights Fungi: Tip-off in Antifungal Chemotherapy

Fungal infections have taken a new spectrum due to the increased incidence of multi-drug resistant fungal pathogens. Freedom of choice for drugs to treat fungal infections is also narrow because of lesser probability of discovering drugs that would bypass affecting human cells and target fungal cells producing fewer side effects in patients. An approach has gained prominence in research is to look for bioactive antifungal compounds from natural sources and discover new classes of antifungals to control the recent emergence of fungal infections. Most of antifungal drugs are originated from fungi. A conservative estimate of total number of fungal species on this planet would exceed 106 if taken into account the ones yet to be discovered from diverse habitats ranging from forest land to marine ecosystem. While attempting to summarize the status of reported fungi-derived antifungal compounds discovered since ancient times, the subset of such compounds were found to be anticancer too. Antifungal compounds with the promise of inducing challenge to rediscover the new effective molecules from drug prototype are also discussed.

Crede’s method in eye water finds a nanomedicine base: a potential candidate to control ophthalmia neonatorum

Abstract Lethal eye infections of newborns occur mostly due to their passage through the contaminated birth canal. In the pre-antibiotic era blindness from such infections was most challenging. This scenario changed after the 1880s with the use of Crede’s method (a drop of 2.0% silver nitrate solution into newborn’s eyes which was later reduced to 1.0%). This research is focused on finding the structure-function relationship between silver nitrate and tears which offer antimicrobial action. A reinvestigation of Crede’s method revealed a light-dependent instant formation of silver oxide nanoparticles (sizes 20–70 nm) with strong antimicrobial action against ocular pathogens. Nano-therapy would be the key reason behind the widely accepted use of silver nitrate eye drop as a prophylactic agent prior to the discovery of antibiotics. A scientific view on the age-old Crede’s method explores the use of nano-therapy as a prophylactic agent. When routine prophylaxis with topical antibiotics brings the risk of resistance, Crede’s method may, in the near future, offer a way to fight against ophthalmia neonatorum (ON) caused by antibiotic-resistant pathogens.

Drying Rate Modeling Through Variable Diffusivity Approach for Vacuum Drying of Onion Slices

Onion is the largest vegetable produced and consumed not only in India but also in the world. It contain generous amounts of a flavonoid called quercetin, in addition to a variety of other naturally occurring chemicals known as organosulfur compounds that have been linked to lowering blood pressure and cholesterol levels. Dehydrated onion can be used as such or it can be converted into powder, granules, flakes, kibbled forms or it can be used to prepare products such as french fried onion rings, salt toasted onion pieces, encased products etc. The key benefits of vacuum drying of onion include lower process temperatures, improved drying rates, and in some case less shrinkage of the product. Onion slices of different thickness viz., 1, 3 and 5 mm were subjected to various temperatures of 50, 60 and 70°C dried under constant vacuum level of 50 mm Hg absolute in order to produce a good quality dehydrated onion. During the drying process, a very short constant rate period was found existing followed by a prominent first and second falling rate periods. The drying rate versus moisture content data fitted well to 3rd degree polynomial with a reasonable accuracy (>0.96). Variable diffusivity approach was applied instead of constant diffusivity and it explained the drying data quite efficiently. Moisture diffusivity of the slices varied from 4.05E-10 to 6.14E-09 m2/s initially and changed continuously with varying moisture content throughout the drying period. However, towards the end of drying it changed from 9.01E-10 to 2.25E-08 m2/s owing to increase in temperature of slice. While concentration dominated the earlier stages of moisture diffusivity and shrinkage played a vital role in the later part.