Journal des bioprocédés et des biotechniques

Rhamnolipid is a new age biosurfactant, commonly produced biotechnologically with Pseudomonas aeruginosa in batch cultivations whereas novel substrates like karanja oil and soybean oil cake were employed, giving yield of 3.609 gm/lit of rhamnolipid, which shows effective and enhanced production of rhamnolipid, compared to other vegetable oil as a carbon sources, mentioned in the literature, at optimised pH of 7.0 and optimised substrate concentration at 3.0%. The optimum yield in terms of substrate was observed as 3.609 gm/lit of rhamnolipid produced per 5.255 ml of oil consumed, while yield in terms of biomass was observed as 3.609 gm/lit of rhamnolipid produced per 2.5 gm of dry biomass. The chloroform:methanol (2:1) extraction system was found to be the best solvent extraction system, where 83% of the rhamnolipid was recovered. The Rhamnolipid was successfully applied for the heavy and toxic metals recovery, where rhamnolipid reduces heavy metal concentration to 73%, 65% and 71% for FeCl₃, ZnSO₄ and Pb(NO₃)₂ respectively, while 43% in the case of toxic metal i.e. NaF. The produced rhamnolipid was found efficient in recovering 31% no-edible oil from oil sludge.

The aim of the research was to evaluate the ability of the fungus Aspergillus niger to produce protease and carry out the deproteinization of shrimp shells and study the effect of adding galactose as an external carbon source at three concentrations (10, 20 and 30% w/w) on the performance of the deproteinization process. The results showed that the 20% galactose concentration was optimum whereas the 10% galactose concentration did not support enough microbial growth and the 30% galactose concentration inhibited the growth of A. niger as was evident from the temperature and carbon dioxide evolution profiles. The temperatures of the shrimp shells and exhaust gas decreased in the first 12 hours (lag) because the heat losses due to evaporation of water (latent heat) and the cooling effect of the inlet air were higher than the heat generation by microorganisms. It then increased as a result of heat accumulation in the bioreactor reaching 28.9- 38.3 and 24.9- 29.0°C, respectively. There was a strong correlation between the concentrations of carbon dioxide in the exhaust gas and the temperature of the shrimp shells. Although the inlet air was humidified, a significant reduction in the moisture content (from 60% to 25.20–43.71%) was noticed by the end of the deproteinization process because the moisture lost through evaporation exceeded the metabolic water production. The pH of the shrimp shells decreased with time to 5.92–6.63 due to acid protease production and then increased to 6.28–8.32 due to the buffering capacity of the calcium carbonate released from the shrimp shells. The protease activity increased from 0.71 U/g to 1.77–1.85 U/g whereas the protein concentration in the shrimp shells decreased from 30.84% to 20.77-25.30 % as a result of protein break down by the proteolytic enzymes produced by A. niger. The chitin concentration in the shrimp shells increased from 16.59% to 20.42-21.99% as a result of protein removal. The highest protease activities, protein removal efficiency and chitin concentration were achieved with galactose concentration of 20%. The spent shrimp shells from the runs that received 10 and 20% galactose concentration had a pale pink-orange color. The existence of the pink-orange color was an indication of the presence of pigments which were not utilized during the fermentation process. The run that received 30% galactose concentration had a gray-black color due to the presence of A. niger spores. The high initial galactose concentration enhanced sporulation of the fungus.

Response surface methodology (RSM) is a powerful tool in the area of process and product improvements. It is a collection of experimental designs and optimization techniques that enables the investigator to determine the relationship between independent variables and the obtained responses. This study focuses on the osmotic dehydration of pumpkin slices using response surface methodology investigating the influences of operating conditions on water loss and solute gain The operating conditions were varied by changing the independent process variables in a range e.g. salt concentrations from 5% to 25% (w/v), salt solution temperatures from 30°C to 70°C and processing time from 30 to 150 minutes. Results showed that all the process variables had significant influences on both water loss and solute gain. However, the solution concentration was observed to be the most influential parameter followed by processing time and solution temperature. The optimum operating conditions that caused maximum water loss and minimum solute gain were found to be at solution temperature of 65.8°C, salt concentration of 25% and processing time of 63 minutes. In conclusion, this study provides a strong guideline for efficient drying of seasonal crop (e.g. pumpkin) in industrial application without compromising quality.

Pectin methylesterase (PME) is the first enzyme acting on pectin, a major component of plant cell wall. PME catalyzes reactions according to the double-displacement mechanism. In plants, PMEs can be classified on the basis of presence or absence of the PRO domain in pectin methylesterase into Type 1 and Type II. Type1 contains one to three PRO domains and two or three introns, type II PMEs are without PRO domain and with five or six introns. Once PMEs are secreted into the cell wall, mature PMEs exhibit three different modes of action: single chain mechanism, multiple chain mechanism and multiple attack mechanism. For bacterial and plant PMEs, single chain and multiple chain mechanism is used and for fungal PMEs only multiple chain mechanism has been proposed. PME activity is regulated by differential expression both spatially and temporally.

Fungal contamination is a significant issue in the food production industry; therefore, identification and characterization of food spoilage fungi would allow for early intervention to limit the amount of fungal contamination, particularly in cereal-based industries. In the present study, culture-dependent and culture-independent methods were applied to study the microbiota of ready-to-eat pizza. The study was pursued by evaluating the effectiveness of a broad-spectrum pulsed ultraviolet light for the decontamination of Penicillium roqueforti (a dominant spoilage mold in bakery products) on the surface of solid agar as a representative of a flat food surface. The average population of mesophilic aerobic bacteria (MAB), mesophilic anaerobic bacteria (MANB), lactic acid bacteria (LAB), molds and yeasts (M+Y) on naturally spoiled pre-cooked pizza were 6.7 ± 0.5, less than 2.3, 2.8 ± 0.6 and 5.4 ± 0.4 log10 CFU g-1, respectively. Cloning and sequencing identified at least 5 genera and species of fungi (Penicillium spp., Saccharomyces spp., Rhodotorula mucilaginosa, Monascus fuliginosus, Galactomyces geotrichum) from 2 phyla (Ascomycota and Basidiomycota). Pulsed light process parameters evaluated were treatment time (1, 3, 5, 7 and 10 min) and voltage input (500, 750 and 1,000 V) at 5 cm distance from the pulsed UV-light. An increase of the input voltage of the lamps and of the duration of the treatment resulted in a higher inactivation of P. roqueforti. The population of P. roqueforti was reduced after 10 min of exposure to pulsed light by 3.74, 5.36 and 6.14 log10 CFU ml^-1 at 500, 750 and 1,000 V, respectively. The inactivation kinetics was best described by the Weibull model (2 parameters) with the smallest root mean squared error (RMSE) and R² ≥ 0.92. The results of this work show that pulsed light is a promising technique for fungi elimination or decontamination in the bakery industry.