Comparison of physicochemical pretreatments of banana peels for bioethanol production

Pretreatments with different concentrations of sulfuric acid (0, 0.5, and 1% v/v) and temperatures (28 and 121 °C at 103 kPa in an autoclave) were performed on banana peels (BP) milled by mechanical grinding and grinding in a blender as well as without grinding. Cellulose, hemicellulose, lignin, ash, and total and reducing sugar contents were evaluated. The highest yields of cellulose enzymatic hydrolysis (99%) were achieved with liquefied autoclaved BP treated with 0.5 and 1% acid after 48 h of hydrolysis. Ethanol production by Kluyveromyces marxianus fermentation was assayed using hydrolyzed BP at 10, 15, and 20% (w/w). The highest ethanol level (21 g/L) was reached after 24 h of fermentation with 20% (w/w) BP. Kinetics of the consumption of reducing sugars under this fermentation condition demonstrates the presence of a lag period (about 8 h). Thus, BP are a good source for ethanol production.     

Biochemical changes during the preservation stage of ripe olive processing

The influences of initial sodium chloride (6% and 0% w/v in tap water) and acetic acid concentrations (0.3%, and 0.6% v/v), use of starter culture, and aerobic versus anaerobic conditions on the biochemical changes that take place throughout the preservation stage of ripe olive processing were investigated. Glucose, fructose and sucrose were completely consumed during preservation. Mannitol and malic acid were metabolized only in the presence of lactic acid bacteria or oxidative yeast (aerobic treatment). The main metabolites produced were lactic and acetic acid in aerobic or anaerobic treatments inoculated with Lactobacillus plantarum. Methanol and ethanol were present in all the brines although in a lower concentration when conditions were aerobic. Thus, induced lactic fermentation led to the most efficient utilization of carbohydrates and yielded the most suitable physicochemical characteristics for ripe olive preservation.     

Isolation of lactic acid bacteria starters from <Emphasis Type="Italic">Jeung</Emphasis>-<Emphasis Type="Italic">pyun</Emphasis> for sourdough fermentation

Lactic acid bacteria (LAB) are key for the fermentation of sourdoughs to improve the quality and nutritive value of bread. The aim of this study was to isolate the LAB starter for sourdough fermentation from Jeung-pyun, a Korean traditional rice cake. Among the twenty two LAB screened, five isolates were selected based on exo-polysaccharide production. Among them, three isolates showed cell growth greater than 8.5 Log CFU/g, maximum increase in the volume of dough, and dextran concentration up to 0.16%. During the sourdough fermentation, pH and total titratable acidity (TTA) were changed, as the three isolates synthesized lactic acid and acetic acid with fermentation quotients less than 2.0. They were identified as Leuconostoc lactis EFEL005, Lactobacillus brevis EFEL004, and Le. citreum EFEL006. They displayed good fermentation properties (growth, dextran production, pH, and TTA) in dough and they are regarded as potential starters to be used in sourdough fermentation.     

Effect of lactic acid fermentation on antioxidant properties and phenolic acid contents of oyster (<Emphasis Type="Italic">Pleurotus ostreatus</Emphasis>) and chanterelle (<Emphasis Type="Italic">Cantharellus cibarius</Emphasis>) mushrooms

Fruiting bodies of Pleurotus ostreatus (oyster) and Cantharellus cibarius (chanterelle) mushrooms underwent acid fermentation using 3 strains of lactic acid bacteria (LAB) as starter cultures. Polyphenol contents, antioxidant activities, and phenolic acid contents in fresh, blanched, and fermented mushrooms were investigated. Fruiting bodies of oyster mushrooms exhibited higher total phenolic contents than chanterelle mushrooms. Blanching caused a decrease in polyphenol contents and antioxidant activities in both mushroom types. No important differences were observed in total phenolic compound contents (measured using Folin-Ciocalteau reagent) in mushrooms using different LAB strains. Lactobacillus plantarum was the most useful microorganism for lactic acid fermentation of fruiting bodies for reduction of the pH value. The highest concentrations of single phenolic acids: gallic, homogentisic, and ferulic acids were present in mushrooms fermented using L. plantarum.     

Phenolic inhibitors involved in the natural fermentation of Gemlik cultivar black olives

Olive fruits of the Gemlik variety harvested from different regions of Turkey were placed in aseptic or non-aseptic brines containing 6 % NaCl. Olives of non-aseptic treatment were left to spontaneously ferment under anaerobic conditions. Samples for microbiological and chemical analysis were taken periodically during the course of the fermentation. No lactic acid bacteria growth was observed in three of the six samples, and yeasts were the prevailing microbial group in the other samples. Brines were analyzed for fermentable substrates (glucose, fructose, sucrose and mannitol), fermentation products (organic acids and ethanol) and phenolic–oleosidic compounds. Most of the unprocessed fruits had a low concentration of oleuropein. Hydroxytyrosol and oleoside 11-methyl ester were the main phenolic and oleosidic compounds in all brines. Likewise, the content of antimicrobials such as the dialdehyde form of decarboxymethyl elenolic acid, either free or linked to hydroxytyrosol, in brines was very low, which may permit the growth of lactic acid bacteria in these media. A growth test with two strains of Lactobacillus plantarum was applied to aseptic brines of all samples to determine whether these compounds inhibited lactic acid bacteria growth. The results of this study indicated that Gemlik olive is a “sweet” variety with a low antimicrobial compound content that can be fermented by lactic acid bacteria under favorable conditions.     

Efficacy of natamycin to control fungal growth in natural black olive fermentation

The effect of natamycin as a fungal control agent in natural black olive fermentation according to the traditional anaerobic system was studied. Black Conservolea olives were subjected to spontaneous fermentation in 8% (w/v) NaCl brine solution (control treatment) or brine supplemented with 0.01% (w/v) natamycin (active compound) for an overall period of 60 days. The changes in the microbial association (lactic acid bacteria, yeasts, Enterobacteriaceae), pH, titratable acidity, organic acids, and volatile compounds were monitored throughout fermentation. The initial microbiota consisted of lactic acid bacteria, yeasts, and Enterobacteriaceae. The addition of natamycin in the brine inhibited the growth of yeasts, without affecting the population dynamics of bacteria, resulting in a more vigorous fermentation with higher titratable acidity compared to spontaneous control process. Moreover, the presence of natamycin inhibited mould spoilage caused by the development of fungal mycelium on the surface of the brine during the traditional anaerobic fermentation system employed widely in Greece in natural black olive processing. Natamycin could be an important component of a processing system to control fungal growth in natural black olive fermentation and at the same time it has the potential to enhance the process by favouring the growth of the indigenous population of lactic acid bacteria against other competing microorganisms.     

Characterization of composition,antioxidant potential and microbial organisms upon submerged <Emphasis Type="Italic">Cicer arietinum</Emphasis> fermentation

The aim of this work was to investigate the composition, antioxidant potential and microbial content of chickpea (Cicer arietinum) steep liquor (CSL) during a submerged fermentation. Chickpea seeds (250 g) were soaked in boiled distilled water (1:2, w/v) for 24 h at 37 °C then filtered and freeze-dried to obtain 8.2 g of CSL. Lysine was the main amino acid accounted for 77.0 % of total free amino acids followed by serine (6.49 %). The results of total amino acids found in CSL indicated that arginine was the main amino acid accounted for 24.0 % of total amino acids followed by tyrosine (20.0 %). Total carbohydrate in the freeze-dried CSL was 1.47 %, wherein reducing sugar was 1.25 % of total carbohydrates. Levels of nicotinic acid, pyridoxine, thiamin, riboflavin, folic acid, and vitamin B₁₂ were 14.3, 3.14, 24.2, 1.11, 0.59 and 24.5 mg/100 mg CSL, respectively. CSL exhibited antioxidant activity (AA) wherein AA was increased with increasing the fermentation time. After 24 h of fermentation, AA of CSL reached 77.0 % while tertiary butyl hydroquinone exhibited 82.0 %. Twenty-five Bacilli isolates were separated from freeze-dried CSL on nutrient broth medium. CSL might be used as an alternative to yeast extract for syngas fermentation because it is rich in nutrients and cheaper compared to yeast extract.     

Potential of a lactic acid bacterial starter culture with gamma-aminobutyric acid (GABA) activity for production of fermented sausage

The ability of lactic acid bacterial starter cultures to produce gamma-aminobutyric acid (GABA) during sausage fermentation was studied. Among 305 strains of lactic acid bacteria isolated from kimchi samples, 11 strains were selected as starter candidates based on the following criteria: growth speed, pH lowering ability, and biogenic amine productivity including GABA-producing activity. During in vitro tests, the Y8 (Lactobacillus brevis), O52, and KA20 strains produced 39.00 ± 1.36, 49.73 ± 3.80, and 64.59 ± 0.61 mg/kg of GABA, respectively. Interestingly, although isolate Y8 showed low productivity in vitro, the GABA content it produced during in situ tests (61.30 ± 2.61 mg/kg) was similar to that produced by isolate PM3 (L. brevis) used as positive control (69.64 ± 2.20 mg/kg). Therefore, isolate Y8 was selected as the best functional starter culture for the production of fermented sausage because it exhibited rapid growth, safety, and abundant GABA productivity.     

Microbial association and acidity development of unheated and pasteurized green-table olives fermented using glucose or sucrose supplements at various levels

Green-table olives, unheated and pasteurized, of Greek cultivar Conservolea were supplemented with glucose or sucrose in various amounts inoculated with Lactobacillus plantarum and fermentation was conducted. Although sugar supplements did not affect the lactic acid bacteria growth rate, they increased the rate of pH drop and the production of acids and lowered the final pH values in all cases. Adequate supplements of sugars (0.5%, 1.0% w v⁻¹), of both types, in unheated olive fermentation, resulted in a fast pH drop, causing a satisfactory halt of Enterobacteriaceae growth in the first days of fermentation, and a subsequent population decline occurred in the following days, eliminating the danger of early stage spoilage and ensuring the safety of the final product. In pasteurized olives, where L. plantarum starter was the only microbial flora, it was considered worth evaluating the fermentation progress without any competition. The rate of pH drop was not as high as in unheated olives, but final pH values and acid development were more pronounced. Lactic acid was the predominant acid developed in both unheated and pasteurized olive fermentation, and increased sugar supplements resulted in faster production and higher yields of this acid. Acetic acid was also produced in low amounts at the end of fermentation, except in the cases of pasteurized olive fermentation supplemented with sucrose, where acetic acid was absent. A switch from homo-fermentative to hetero-fermentative metabolism might have taken place in case of glucose presence, but the same was not observed for sucrose.     

Effect of millimeter waves on the microbiological and physicochemical properties of Korean rice wine <Emphasis Type="Italic">Makgeolli</Emphasis>

Millimeter waves are electric waves between 30 and 300 GHz. They are known to affect microbial growth. Here, the effects of millimeter waves on the microbiological and physicochemical properties of Makgeolli irradiated during fermentation were investigated. Millimeter waves at 60 and 70 GHz were used, and the fermentation was carried out at 30°C. The numbers of both lactic acid bacteria and yeasts have changed with similar pattern each then during the fermentation, but the effect of milimeter wave treatment was not critical as growth patterns were independent of both irradiation period and wave frequency. Furthermore, pH and total acidity did not change during fermentation. Although irradiation drastically increased sugar production during the initial stage of fermentation, the change was not frequency dependent. At the end of fermentation, the alcohol content in irradiated Makgeolli was definitely higher than that in un-irradiated Makgeolli, and the difference was frequency dependent.     

Tuna Burgers Preserved by the Selected <Emphasis Type="Italic">Lactobacillus paracasei</Emphasis> IMPC 4.1 Strain

The use of protective microbial strains in combination with modified atmosphere packaging (MAP) and refrigerated storage on the shelf life of tuna burgers was investigated. Preliminary, the protective ability of three lactic acid bacteria (LAB) cultures (Lactobacillus casei, Lactobacillus paracasei, and Lactobacillus plantarum) have been assessed on ready-to-cook tuna burgers. Among them, L. paracasei showed the best preserving performance and significantly controlled both aerobic mesophilic bacteria and Pseudomonas spp. growth. Subsequently, the efficacy of the selected LAB culture under MAP conditions (5% O₂ and 95% CO₂) was assessed evaluating microbial and sensory quality, as well as volatile aldehyde content. Results indicated that the shelf life of burgers containing L. paracasei and packaged under MAP was 4 days longer than the control (shelf life about 6 days) and that the applied procedure represents an effective approach for the mild preservation of fish products.     

Probiotic lactic acid bacteria isolated from traditional Korean fermented foods based on β-glucosidase activity

This study was designed to isolate lactic acid bacteria (LAB) with β-glucosidase activity and probiotic properties from Korean fermented foods. Among nine isolates, four LAB strains had excellent survival rates at pH 2.5 with 0.3% (w/v) pepsin for 3 h and 0.3% (w/v) oxgall for 24 h. Four LAB strains did not produce β-glucuronidase and showed adhesion ability to HT-29 cells that was superior to that shown by the reference strain Lactobacillus rhamnosus GG. All four strains were sensitive to ampicillin, tetracycline, chloramphenicol, and doxycycline. These strains were identified as Leuconostoc mesenteroides H40, Lactobacillus plantarum FI10604, L. brevis FI10700, and L. perolens FI10842 by 16S rRNA gene sequence, respectively. It was found that L. perolens FI10842 produced the highest β-glucosidase activity (49.10 mU/mL). These results indicate that the four LAB strains could be used as potential probiotic. Especially L. perolens FI10842 could be used as a starter culture for fermentation.     

Antioxidant properties of a vegetable–fruit beverage fermented with two <Emphasis Type="Italic">Lactobacillus plantarum</Emphasis> strains

Fermented vegetable–fruit beverages are a popular fermented food, with many potential health benefits. In this study, two commercial Lactobacillus plantarum strains were selected to ferment a beverage containing apples, pears, and carrots. The metabolites and antioxidant activities were examined during the fermentation process. Results showed that lactic acid and acetic acid accumulated gradually, whereas malic acid decreased. Glucose and fructose increased from 0.48 and 14.8 g/L to 7.7 and 20.8 g/L, respectively, while sucrose decreased slightly. Ascorbic acid also increased continuously during the fermentation to 90.74 mg/100 mL. DPPH and ABTS radical scavenging activity and FRAP reached their maximum value after 4–8 days. The accumulation of TPC, TFC, and SOD reached their maximum value on the 8th day of fermentation. Our study revealed that the L. plantarum-fermented vegetable–fruit beverage showed significant antioxidant activity, which is helpful in evaluating the fermentation end-point and developing a high-quality fermented beverage.     

Preserving Melons by Osmotic Dehydration in a Ternary System Followed by Air-Drying

In this study, the effect of different osmotic solution concentrations (20–60% w/w of sucrose with 10% w/w NaCl salt), fruit to solution ratios (1:9–1:3), immersion times (0.5–4 h), and temperatures (15–55°C) on the mass transfer kinetics during osmotic dehydration of melons (Curcumis melo L.) in ternary solution namely sucrose–salt–water followed by air-drying were investigated. The effective diffusion coefficients for sucrose and water during osmotic dehydration were determined, assuming osmotic dehydration to be governed by Fickian diffusion. The estimated parameters allowed optimizing the system to reduce total processing time. The optimum treatments were with 50% sucrose and 10% NaCl salt concentration, fruit to solution ratio of 1:4 for 1 h at 45°C. Samples non-treated and pre-treated in optimized conditions were dried in a hot-air dryer at 60°C until equilibrium was achieved after 2.5 h. Pre-treatment reduced the air-drying period in up to 6.8 h.     

Effect of sodium selenite on the bacteria growth,selenium accumulation,and selenium biotransformation in <Emphasis Type="Italic">Pediococcus acidilactici</Emphasis>

In this study, the effect of low selenium concentrations on bacteria growth, selenium bioaccumulation, and selenium speciation in Pediococcus acidilactici was investigated. Six different sodium selenite (Na₂SeO₃) solutions with concentrations of 0, 0.5, 1, 2, 3, and 4 mg/L were added in MRS broth for 24 h. Then, the obtained bacterial pellets were weighed. The contents of total selenium and selenium species in the bacterial pellets were measured via optimized enzymatic hydrolysis and HPLC-ICP-MS. The maximum dried P. acidilactici biomass of 1.44 g/L was achieved by utilizing 1 mg/L Na₂SeO₃. By increasing sodium selenite concentrations, total selenium contents were significantly increased from 0.14 to 1.45 mg/g dry weight (p < 0.05). The findings indicated that selenium was favorably incorporated into the bacteria protein fraction and mainly formed selenocysteine. Therefore, selenium-enriched lactic acid bacterium P. acidilactici can deliver a less-toxic, more bioavailable selenium source for human and animal nutrition.     

Efficient very‐high‐gravity fermentation of sugarcane molasses by industrial yeast strains

In this study industrial strains were inoculated, in successive cycles, at high cell density into a sugarcane‐based juice containing normal (22%, w/v) and very high sucrose (30%, w/v) levels and supplemented with peptone as a nitrogen source. At 30 °C, in shaken cultures, in the normal gravity situation, efficient sucrose utilization occurred in both the supplemented and unsupplemented medium. At higher sugar concentrations, supplementation with peptone induced a more efficient fermentation compared with the unsupplemented medium, with higher biomass accumulation and maintenance of cell viability, and ethanol levels as high as 16% (v/v). Trehalose was also high during the cycles, probably as a necessary response of the yeast to the high stress fermentation conditions. This suggests that it is possible to increase ethanol production by using very‐high‐fermentation technology and that nutritional supplementation would have a positive effect on the fermentation, allowing for efficient sugar consumption and cell viability maintenance. Copyright © 2016 The Institute of Brewing & Distilling     

Modeling and Optimization of Lactic Acid Production using Cashew Apple Juice as Substrate

The production of lactic acid by Lactobacillus casei B-442 was studied and modeled. Sugar feedstock was provided using cashew apple juice, an alternative glucose and fructose feedstock that proved to yield high concentrations of lactic acid. The fermentations were carried out in a 1-L fermenter under constant agitation (150 rpm) and controlled pH (6.5). Lactic acid production was evaluated through a dynamic study, varying the initial concentration of sugar in the range of 20 to 60 g/L. Biomass, reducing sugars, and lactic acid concentration were measured throughout the experiments. The highest production of lactic acid (59.3 g/L) was obtained operating the fermentation with 60 g/L of reducing sugar from the cashew apple juice. A rigorous kinetic model was developed for batch fermentation of cashew apple juice for lactic acid production by L. casei B-442. The growth of biomass and lactic acid production were affected by substrate limitation, substrate inhibition and lactic acid inhibition. The model assumed growth- and non-growth-associated lactic acid production and a term for microorganism death was also included in the model. Parameters of the kinetic model were determined based on experimental data by using the least mean squares method and Levenberg–Marquardt algorithm. The model validation was performed and the model was statistically able to fit the profiles for growth of biomass, sugar consumption and lactic acid production. The optimization of the process, using the model, was carried out and the optimum operating conditions aiming highest productivity, lowest production cost and highest gross profit are presented.     

复合乳酸菌发酵蓝莓黑莓混合汁过程中的品质变化

以鲜榨并经灭菌的蓝莓黑莓混合果汁为原料,接入3种不同的乳酸菌（植物乳杆菌、乳酸乳杆菌、肠膜明串珠杆菌）进行发酵,研究发酵过程中乳酸菌活菌数、pH、总酸、总糖、还原糖、总酚、体外抗氧化和抑菌活性变化规律。结果表明,乳酸菌在混合果汁中生长良好,24 h时活菌数最高,为1.23×108 cfu/mL;发酵过程中,pH值不断降低,由最初的5.50降低到3.75,总酸含量呈不断上升趋势,从初始含量0.15 g/100 mL上升到2.15 g/100 mL;还原糖呈先短暂上升然后下降趋势,发酵至6 h为最高值2.63 g/L,总糖被微生物利用消耗, 质量浓度不断下降,42 h后趋于0 g/L;总酚含量从2.32 mg/mL升高到3.26 mg/mL,发酵前后增加了40.52%;DPPH·、羟基自由基和超氧阴离子自由基清除能力比未发酵前分别提升了18.17%、30.67%和34.55%。发酵混合汁对大肠杆菌、金黄色葡萄球菌、酿酒酵母和黑曲霉等几种微生物的抑菌作用显著,抑菌效果随发酵时间而逐渐提高。因此,利用复合乳酸菌发酵来提升蓝莓黑莓混合汁品质和开发功能性产品具有重要意义。     

Optimization of Trehalose Production by <Emphasis Type="Italic">Rhodotorula dairenensis</Emphasis> Following a Sequential Strategy of Experimental Design

Initially, a technical screening was applied to select yeasts with a potential for trehalose production using thermal stress for the induction of synthesis. The effects of the concentrations of sugar cane molasses, corn steep liquor and a commercial yeast extract Prodex Lac SD®, and of pH and temperature on the biomass were studied using a fractional design followed by a central composite rotatable design (CCRD). The optimum values were 50 g/l for the molasses and corn steep liquor concentrations, initial pH of 5.5, and temperature of 30 °C, with no yeast extract. Under these conditions, the production of trehalose was studied using a CCRD to optimize the temperature (33 to 47 °C) and exposition time (60 to 120 min) of the cultures to the thermal stress. The maximum intracellular trehalose content reached was 20.5% (g trehalose/100 g dry cell) at temperatures of 35–40 °C and with 100–120 min of exposition time to the thermal stress.     

A study on the implications of NaCl reduction in the fermentation profile of Conservolea natural black olives

This study examined the impact of different mixtures of NaCl, KCl, and CaCl₂ on the fermentation profiles of Conservolea natural black olives. Five different combinations of chloride salts were investigated, namely (i) 8% NaCl (control treatment), (ii) 4% NaCl and 4% KCl, (iii) 4% NaCl and 4% CaCl₂, (iv) 4% KCl and 4% CaCl₂, and (v) 2.6% NaCl-2.6% KCl-2.6% CaCl₂. The changes in the microbial association (lactic acid bacteria, yeasts, Enterobacteriaceae), pH, titratable acidity, organic acids, volatile compounds, and mineral content in olive flesh were analyzed. Results demonstrated that all salt combinations led to vigorous lactic acid processes based on the obtained values of pH (3.9-4.2) and titratable acidity (0.70-0.86 g lactic acid per 100 ml brine). Organoleptic evaluation was a critical factor in the acceptability of the final product. Increasing concentrations of CaCl₂ or a combination of KCl and CaCl₂ rendered the product bitter with low acceptability by the taste panel. Only one combination of chloride salts (4% NaCl and 4% KCl) could finally produce olives with lower sodium content and good organoleptic attributes. The results of this study could be employed by the Greek table olive industry in an attempt to produce natural black olives with less sodium without affecting the traditional taste of fermented olives in order to meet consumers’ demand for low sodium dietary intake.