A welded steel protective cover used for the heat treatment of steel sheet coils is investigated. The protective cover is made of austenitic stainless steel and consists of three main segments, welded together, which have 1400 mm height each. The plate thicknesses at the lower, middle and upper segments are different. The investigation aimed to improve the lifetime and the number of heat cycles of the protective cover by changing the geometry, the effect of the thicknesses and the material. Damaged covers have been evaluated, made calculations of stress and deformations, and carried out a series of finite element simulations. Both horizontal and vertical corrugated sheets were simulated and compared. The non-corrugated plates were also investigated, but their performance was behind the corrugated ones. The original geometry and that of the horizontal corrugated plate are identical from the stress level point of view. The vertical position of the corrugated plate provided a better result than the horizontal one. The calculated and simulated results for the original geometry are close to the measured damage.
Protein hydrolysis using immobilized proteases may present problems, which are mainly caused by the diffusion of macromolecular substrate. Pre-hydrolysed substrate could be a viable alternative in this process. The aim of this work was to test the casein and β-lactoglobulin hydrolysis using immobilized papain on glyoxyl-agarose, following substrate pre-treatment with immobilized trypsin. Although immobilized papain showed difficulties to degrade the milk proteins, after 10 min of trypsin pre-hydrolysis, the immobilized papain was able to achieve the maximum degree of hydrolysis in shorter time. For pre-hydrolysate casein, the immobilized papain reached 98.9% at 60 min total reaction (including the 10 min pre-digestion). As for β-lactoglobulin, immobilized papain was capable of achieving maximum levels after just 60 min of reaction, where the free enzyme only achieved 60% of its maximum. Pre-hydrolysis with trypsin appears to have worked well as a pre-treatment method to increase the proteolytic action of immobilized papain.
Authors:S. Dragoev, D. Balev, G. Ivanov, B. Nikolova-Damyanova, T. Grozdeva, E. Filizov, and K. Vassilev
Lipid oxidation is one of the main factors responsible for the quality loss in refrigerated and frozen stored fish products. The aim of the study was to evaluate the effect of superficial treatment of Atlantic salmon (Salmo salar) with dihydroquercetin (DHQ) solutions on the hydrolytic and oxidative changes in fish lipids during refrigerated storage. It was found that treatment with DHQ solution (1.0 g l−1) reduced approximately twice the free fatty acids content of chilled stored salmon. After 11 days of storage at 1 °С, the contents of hydroperoxides (HPO) and 2-thiobarbituric acid reactive substances (TBARS) of these samples decreased with 45.00 and 0.91 mg MDA/kg, respectively. The share of saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), and polyunsaturated fatty acids (PUFA) in control and experimental samples did not differ significantly (P>0.05). Results obtained show that the superficial treatment of salmon with DHQ solution (1.0 g l−1) delayed the hydrolytic and oxidative changes in fish lipids significantly, thus preserving the salmon freshness up to 11 days of storage at 1 °С.
The effect of organic acids on the melanosis inhibition and shelf-life on shrimp was investigated. Shrimps were treated with 1% solutions of lactic, citric, acetic acids, sodium metabisulfite (0.3%) and their various combinations. After treatments the shrimps were stored at 4 °C and evaluated for melanosis every day and quality changes on every other day. Combinations with sodium metabisulphite were the most effective in delaying melanosis. Citric and lactic acids extended shelf life to a lesser extent but acetic acid had no effect.
Authors:S.A. Aouanouk, A. Mouheb, R. Absi, and R. Zazoun
A major problem related to heat treatment of milk is formation of deposits. This is due to the chemical alteration of β-lactoglobulin protein that leads to formation of coatings on the walls of the equipment. These deposits induce losses in the thermal performance of the heat exchanger. In order to provide an adequate prediction of these deposits, we present a two-dimensional (2D) modelling study of the channel of a plate heat exchanger. Compared with the former studies, where the domain is related to a single plate, our work is related to the area between the two plates. This approach will allow a better understanding and description of the evolution and behaviour of β-lactoglobulin protein. Equations for fluid flow, energy, and fouling were resolved. Special boundary conditions had been implemented to link the amount of deposits with thermal transfer. Predicted results for the amount of fouling deposit on the wall were validated by comparisons with experimental data available in literature. The behaviour of β-lactoglobulin protein was studied by analyzing its distribution in the channel.
Authors:Zsanett Bodor, Bianka Pergel, and Csilla Benedek
., 2009; Kaszab et al., 2017 ). The properties of honeys also vary according to their exposure to heat. Heat treatment of the honey can influence its composition and physicochemical properties ( Bodor et al., 2019; Božiková et al., 2018 ). The proper
Authors:L. Silva, G. Maia, P. Sousa, R. Figueiredo, M. Afonso, M. Gonzaga, C. Gomes, and E. Figueiredo
The purpose of this experiment was to evaluate the effect of heat treatment on the rheological properties of mixed nectars, based on cashew apple, mango, and acerola pulps. Ten different formulations with different mass fractions of cashew apple, mango, and acerola pulps were prepared using a simplex centroid design [with a total of 35% (w/w) pulp] and submitted to heat treatment at 90 °C for 1 min. Samples were collected before and after heat treatment and characterization of their rheological properties was carried out. The rheological behaviour was obtained at 25 °C, with shear rate ranging from 108 to 500 s−1 (upward curve) and from 500 to 108 s−1 (downward curve) for 1 min with 25 readings for each curve. The Ostwald de Waele model showed to be a good fit for all formulations studied, which showed a non-Newtonian behaviour and a pseudoplastic character. Results of apparent viscosity for the non-heated formulations were well fitted by the linear model and the heat treated formulations by the cubic model. The heat treated formulations had higher (P<0.05) values of consistency index and apparent viscosity, as well as lower (P<0.05) values of flow behaviour index compared to non-heated formulations. The rheological characterization of these formulations is a very useful tool during product development and processing control of mixed nectars of fruit juice.