Effect of low oxygen stress on the metabolic responses of tomato fruit cells.

Postharvest losses of fruits and vegetables can occur due to cell breakdown and browning during controlled atmosphere storage as a result of low oxygen (O2) stress. Therefore, the study was designed to better understand the underlying mechanisms of the response of isolated tomato fruit cells incubated at low O2 (hypoxic and anoxic) conditions as a model system. The O2 stress conditions used for the experiment were based on the results of the Michaelis-Menten constant (Km) of respiration. A total of 56 polar metabolites belonging mainly to different functional groups, including amino acids, organic acids, sugars and sugar alcohols, were identified using GC-MS. O2 stress stimulated the biosynthesis of most of the free amino acids while decreasing the synthesis of most of the organic acids (especially those linked to the tricarboxylic acid cycle), sugars (except for ribose) and other nitrogen-containing compounds. The down-regulation of these TCA cycle metabolites served to provide energy to ensure the survival of the cell. Increases in the sugar alcohol levels and induction of fermentative metabolism were observed under low O2 stress. By employing multivariate statistics, metabolites were identified that were essential to the oxygen stress response and establishing the correlation between metabolite abundance, oxygen levels, and incubation period were achievable. A higher correlation was observed between the O2 levels and most of the metabolites.

Development and performance evaluation of an improved electric baking oven for baked products.

An improved electric baking oven was designed and fabricated using locally available materials for baking cakes and biscuits. Provisions of necessary adjustments were employed for ensuring uniform distribution of heat in all trays of the baking chamber. Its baking characteristics in terms of baking time, specific volume, and product quality in terms of sensory attributes were evaluated. The oven was found to be quite satisfactory in functioning for baking cakes and biscuits. Total time was only 15-28 min for baking the cake samples in the oven. On the other hand, comparatively, a bit longer time 18-35 min required for baking the biscuit samples. Baking cost was lesser in baking small-sized cakes and biscuits than those of large sized. The quality of baked products was better in terms of taste, color, flavor, texture, and appearance than ordinary market products. Loaf volume of each cake (with 4 × 5 × 8 cm3) was 100%, which gave specific volume of 652.8 cm3/kg. Similarly, the specific volume of biscuits was 810 cm3/kg. The electric baking oven is quite efficient in baking quality cakes and biscuits uniformly, which can be provided to rural small entrepreneurs for commercial manufacturing of biscuits and cakes.

Heat-Induced Interaction of Milk Proteins: Impact on Yoghurt Structure.

Heating milk for yoghurt preparation has a significant effect on the structural properties of yoghurt. Milk heated at elevated temperature causes denaturation of whey protein, aggregation, and some case gelation. It is important to understand the mechanism involved in each state of stabilization for tailoring the final product. We review the formation of these complexes and their consequence on the physical, rheological, and microstructural properties of acid milk gels. To investigate the interactions between denatured whey protein and casein, the formation of covalent and noncovalent bonds, localization of the complexes, and their impact on ultimate gelation and final yoghurt texture are reviewed. The information regarding this fundamental mechanism will be beneficial to develop uniform quality yoghurt texture and potential interest of future research.

High carbon-di-oxide modified atmospheric packaging on quality of ready-to-eat minimally processed fresh-cut iceberg lettuce.

Fresh-cut lettuce is a very well-known salad for today's routines because it obliges minimal preparation to minimize the loss of health beneficial vitamins, minerals, antioxidants and other phytochemicals. It is a prodigious challenge to serve its consumers fresh. Quality of freshly processed lettuce under high CO2 modified atmosphere packaging (MAP) has been investigated as a realistic alternative technique for its preservation. Storage under high CO2 atmospheric treatments exhibited a significant impact in microbial development, electrolyte leakage, volatile metabolites and sensory quality of fresh-cut iceberg lettuce. This storage condition (MAP 1: 5 kPa O2 and 20 kPa CO2 balanced by N2 at 7 °C for 6 days) inhibited the growth of mesophilic bacteria and yeasts; delayed the enzymatic browning (cut-edges and intact surface) of fresh-cut iceberg lettuce and overall visual quality was also in acceptance limit. The development of off-odors was perceived in high CO2 MAP as a consequence of volatiles (ethanol and acetaldehyde) accumulation which was persisted at an inexcusable level during 6 days of storage periods.

Effect of milk pH at heating on protein complex formation and ultimate gel properties of free-fat yoghurt.

The effect of milk pH before heating on casein-whey protein interactions and ultimate gel properties of the free-fat yoghurt was investigated. Reconstituted skim milk at different pH values (6.4, 6.8 and 7.2) was heated at 80 °C for 30 min. The type of protein and size of casein micelle in milk were determined. The storage modulus (G'), loss tangent (tan δ), flow behaviour as well as microstructure, firmness and water holding capacity of the yoghurt samples were measured. Heating milk at pH 7.2 formed mostly soluble protein complexes whereas at pH 6.4 micelle bound complexes was dominant. However, heating milk at pH 6.8 resulted in a relatively compact protein network due to a balanced contribution from both soluble protein/κ-casein complexes and whey protein-casein micelle associated complexes. Yoghurt prepared with milk heated at pH 6.8 showed significantly higher G' values, shorter gelation times, higher water holding capacity, firmness and more compact protein network compared to those at pH 6.4, 7.2 and unheated milk. The obtained results demonstrated that milk pH adjustment before heating could be an important factor governing uniform quality yoghurt production.