Selection of Saccharomyces cerevisiae strains for efficient very high gravity bio-ethanol fermentation processes

An optimized very high gravity (VHG) glucose medium supplemented with low cost nutrient sources was used to evaluate bio-ethanol production by 11 Saccharomyces cerevisiae strains. The industrial strains PE-2 and CA1185 exhibited the best overall fermentation performance, producing an ethanol titre of 19.2% (v/v) corresponding to a batch productivity of 2.5 g l-1 h-1, while the best laboratory strain (CEN.PK 113-7D) produced 17.5% (v/v) ethanol with a productivity of 1.7 g l-1 h-1. The results presented here emphasize the biodiversity found within S. cerevisiae species and that naturally adapted strains, such as PE-2 and CA1185, are likely to play a key role in facilitating the transition from laboratory technological breakthroughs to industrialscale bio-ethanol fermentations.Fundação para a Ciência e a Tecnologia (FCT) - PTDC/BIO/66151/2006, SFRH/ BD/64776/2009, SFRH/BPD/44328/ 200

Emerging green techniques for the extraction of antioxidants from agri-food by-products as promising ingredients for the food industry

Nowadays, the food industry is heavily involved in searching for green sources of valuable compounds, to be employed as potential food ingredients, to cater to the evolving consumers’ requirements for health-beneficial food ingredients. In this frame, agri-food by-products represent a low-cost source of natural bioactive compounds, including antioxidants. However, to effectively recover these intracellular compounds, it is necessary to reduce the mass transfer resistances represented by the cellular envelope, within which they are localized, to enhance their extractability. To this purpose, emerging extraction technologies, have been proposed, including Supercritical Fluid Extraction, Microwave-Assisted Extraction, Ultrasound-Assisted Extraction, High-Pressure Homogenization, Pulsed Electric Fields, High Voltage Electrical Discharges. These technologies demonstrated to be a sustainable alternative to conventional extraction, showing the potential to increase the extraction yield, decrease the extraction time and solvent consumption. Additionally, in green extraction processes, also the contribution of solvent selection, as well as environmental and economic aspects, represent a key factor. Therefore, this review focused on critically analyzing the main findings on the synergistic effect of low environmental impact technologies and green solvents towards the green extraction of antioxidants from food by-products, by discussing the main associated advantages and drawbacks, and the criteria of selection for process sustainability

Extraction of phenolic compounds from bilberry by-products left after pulsed electric field assisted juice production

By-products (press cake) resulting from PEF assisted juice production might still be exploited for recovery of valuable compounds. Therefore, the aim of this work was to investigate the effect of PEF pre-treatment of bilberry fruits on the recovery of phenolic compounds from the press cake left after the juice pressing. Mechanical pressing was used for juice extraction. The experiments were carried out at constant pressure (1.32 bar) using a lab-designed pressing chamber. PEF pre-treatments of constant electric field strength (3kV/cm) and varying specific energy (1-10 kJ/kg) or varying electric field strength (1-5 kV/kcm) and constant specific energy (10 kJ/kg) were applied to fresh bilberries prior to their pressing. Then the press cake left after the juice production was subjected to further extraction with acidified aqueous ethanol for 24 hours at ambient temperature. The total phenolic content of the extracts was determined using the Folin-Ciocalteu method [1]. The antioxidant activity of the extracts was tested using the FRAP assay [2]. Significantly higher amounts of total phenolics were extracted from the press cake of PEF-treated bilberries. The content of phenolic compounds extracted from the press cake of untreated (control) berries was 942 mg/100 g. The application of a PEF pre-treatment at 1, 3 and 5 kV/cm and constant specific energy yielded an increase in total phenolic content by 36%, 63% and 89%, respectively. When PEF pretreatment of constant electric field strength but varying energy input was applied to berries the total phenolic content in the press cake extracts was 58%, 56% and 63% higher for 1, 5 and 10 kJ/kg energy input, respectively. The PEF pre-treatment also resulted in significantly higher ferric reducing antioxidant power of the press cake extracts. In comparison to the control extract, PEF pre-treatments of berries at 1, 3 and 5 kV/cm increased the FRAP values of their press-cake extracts by 44%, 71% and 80%, respectively. Similarly, FRAP of press cake extracts obtained from PEF-treated bilberries at fixed electric field but varying energy input was from 40% (1 kJ/kg) to 71% (10 kJ/kg) higher. The results obtained from this study demonstrate that PEF pre-treatment of bilberries at higher intensity, both in terms of higher electric field strength or higher specific energy at fixed electric field strength resulted in better extractability of phenolic antioxidants from bilberry press cake left after the juice pressing. However, the increase in electric field strength had stronger impact on the extraction efficiency than the increase in delivered specific energy

Effect of high-voltage electrical discharge (HVED) at high frequency on vacuum freeze-drying time and physicochemical properties of blueberries

Vacuum freeze-drying provides high-quality food products. However, it requires long operating times and high energy consumption. High voltage electrical discharge (HVED) is an emerging technology that could enhance freeze-drying rates and final product quality. This study aimed to evaluate the effect of HVED at high frequency (200 kHz) on freeze-drying kinetics of blueberries (effective moisture diffusivity, drying times) and the physicochemical properties of the resulting freeze-dried fruits. Blueberries were pretreated at different electric field strengths (10, 20, and 30 kV/cm) and operational times (10, 20, and 30 s) and freeze-dried until constant weight. The HVED treatment at 30 kV/cm and 30 s exhibited the best moisture diffusivity values and reduced drying time by at least 30% compared with untreated samples. Samples treated with HVED and freeze-dried preserved their shape and prevented shrinkage. Applying HVED as a pretreatment electrotechnology can help improve the efficiency of freeze-drying and the quality of dried food products

Extraction of phenolic antioxidants from by-products left after the pulsed electric field assisted juice production

By-products resulting from pulsed electric field (PEF) assisted juice production might be exploited for recovery of valuable phytochemicals. The aim of the work was to investigate the effect of PEF pre-treatment of raspberry, bilberry and black currant berries on the recovery of phenolic compounds from the press cakes left after the juice pressing. Fresh berries were mechanically pressed using a lab-designed pressing chamber. PEF pre-treatments of varying electric field strength and specific energy input were applied to berries prior to juice pressing. The press cakes left after the juice production were subjected to further extraction with acidified aqueous ethanol. The total phenolics (TP), anthocyanins (TA) contents, and antioxidant activity of the extracts were analyzed. Significantly higher amounts of TP and TA were extracted from the press cakes of PEF-treated berries. For raspberry press cake extracts an increase in TP content was in the range of 6-22% (3kV/cm 12kJ/kg and 3kV/cm 1kJ/kg treatment, respectively), for black currant press cake extracts – in the range of 55-69% (1kV/cm 10kJ/kg and 0.5kV/cm 10kJ/kg treatment, respectively) and for bilberry press cake extracts - 36-89% (1kV/cm 10kJ/kg and 5kV/cm 10kJ/kg treatment, respectively). The extracts from press cakes obtained after PEF assisted juice pressing had stronger ferric reducing antioxidant power (FRAP). In comparison to the untreated samples, PEF pre-treatment of raspberries, black currants and bilberries increased FRAP of their press cake extracts by up to 24%, 61% and 80%, respectively. The data obtained in this study demonstrate that PEF pre-treatment of berries resulted in better extractability of phenolic antioxidants from the press cakes left after the juice production. PEF pre-treatment at higher intensity resulted in better extractability of bioactive compounds from bilberry press cake, but for raspberries and black currants the enhancement of phenolic compounds extraction did not correlate with the applied PEF treatment intensity