• Energy Research

Oenococcus oeni ATCC 23279 cells immobilized on delignified cellulosic material (DCM) were used for malolactic fermentation (MLF). In first, eleven repeated alcoholic fermentation batches of white must of 11-12 degrees Be initial density were performed by Saccharomyces cerevisiae cells immobilized on delignified cellulosic material at 20 degrees C. Subsequently, the induction of MLF in the eleven taken wine batches by O. oeni cells immobilized on DCM took place at 27 degrees C. From the 3rd MLF batch up to 10th, the malic acid degradation was 53.1 up to 67.4% and the cfu of the immobilized cells/g of biocatalyst remained stable. The produced lactic acid was less than the stoichiometric yield and acetic acid content was significantly reduced after MLF not contributing in an important increase of the volatile acidity of wine. Ethanol, higher alcohols acetaldehyde and diacetyl contents in wines after MLF were in acceptable levels.

Abstract:  The natural mixed culture kefir was immobilized on boiled corn grains to produce an efficient biocatalyst for lactic acid fermentation with direct applications in food production, such as sourdough bread making. The immobilized biocatalyst was initially evaluated for its efficiency for lactic acid production by fermentation of cheese whey at various temperatures. The immobilized cells increased the fermentation rate and enhanced lactic acid production compared to free kefir cells. Maximum lactic acid yield (68.8 g/100 g) and lactic acid productivity (12.6 g/L per day) were obtained during fermentation by immobilized cells at 37 °C. The immobilized biocatalyst was then assessed as culture for sourdough bread making. The produced sourdough breads had satisfactory specific loaf volumes and good sensory characteristics. Specifically, bread made by addition of 60% w/w sourdough containing kefir immobilized on corn was more resistant regarding mould spoilage (appearance during the 11th day), probably due to higher lactic acid produced (2.86 g/Kg of bread) compared to the control samples. The sourdough breads made with the immobilized biocatalyst had aroma profiles similar to that of the control samples as shown by headspace SPME GC‐MS analysis.

Lactic acid production using Kluyveromyces marxianus (IFO 288), Lactobacillus delbrueckii ssp. bulgaricus (ATCC 11842) and Lactobacillus helveticus (ATCC 15009) individually or as mixed culture on cheese whey in stirred or static fermentation conditions was evaluated. Lactic acid production, residual sugar and cell biomass were the main features examined. Increased lactic acid production was observed, when mixed cultures were used in comparison to individual ones. The highest lactic acid concentrations were achieved when K. marxianus yeast was combined with L. delbrueckii ssp. bulgaricus, and when all the strains were used revealing possible synergistic effects between the yeast and the two lactic acid bacteria. The same synergistic effects were further observed and verified when the mixed cultures were applied in sourdough fermentations, proving that the above microbiological system could be applied in the food fermentations where high lactic acid production is sought.

In the frame of efforts to add value to the Mediterranean currant cultivation and processing sectors, which is essential for their sustainability, sweet wine production is proposed from the finishing side-stream (FSS) of premium quality Corinthian currants, involving complete fermentation using an alcohol-tolerant yeast followed by (i) the addition of FSS to extract sugars or (ii) syrup made from FSS to adjust sweetness. Wine was also made by (iii) ceasing fermentation at the desired sugar level by ethanol addition. The non-fortified wines had 15.2–15.5% ethanol, 115–145 g/L residual sugar, 7.2–7.6 g/L titratable acidity, low volatile acidity (VA; <0.33 g/L), 280–330 mg/L phenolic content (TPC) (as gallic acid), and 23.8–35.6 mg/L antioxidant capacity (AC) (as ascorbic acid). In total, 160 volatiles were identified by SPME GC-MS, including compounds derived from the grapes, the raisin drying, and the fermentation process. The non-fortified wines had better characteristics (mainly VA, AC, and TPC) than the fortified wine, while sweetness adjustment by FSS is the simplest and lowest cost method since it does not involve ethanol or syrup addition. The proposed methods can lead to good quality sweet wines with a characteristic fruity (grape/raisin) flavor that could be commercialized as specialty raisin beverages or liqueurs.