Effect of Lactate on the Growth and Production of Diacetyl and Acetoin by Lactobacilli

Diacetyl and acetoin production and cell growth in Lactobacillus acidophilus CNRZ 232, Lactobacillus casei ssp. rhamnosus ATCC 7469, Lactobacillus brevis ATCC 14869, and Lactobacillus fermentum ATCC 9338 were studied. The first three species produced large amounts of diacetyl and acetoin when pyruvate was included in a medium with yeast extract, peptone, tryptone, and glucose. Lactobacillus fermentum failed to produce the compounds under consideration.Lactobacillus acidophilus, Lactobacillus casei, and Lactobacillus brevis utilized lactate as a carbon source. When lactate was added to the medium containing pyruvate, the diacetyl, acetoin, and biomass decreased in Lactobacillus casei and Lactobacillus brevis. In Lactobacillus acidophilus both compounds decreased somewhat, and bacterial growth increased, although it decreased again at high lactate concentrations. There was no production of diacetyl and acetoin at pH lower then 4.25 and only little at 4.25.     

Influence of compounds associated with fermented dairy products on the growth of lactic acid starter and probiotic bacteria

The growth of 24 strains of lactic acid starter bacteria (Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus and Lactococcus lactis) and 24 strains of probiotic bacteria (Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus paracasei, Lactobacillus rhamnosus and bifidobacteria) in liquid media containing different substances was assessed. The substances used were salts (NaCl and KCl); sugars (sucrose and lactose); sweeteners (acesulfame and aspartame); aroma compounds (diacetyl, acetaldehyde and acetoin); natural colorings for fermented milk (red, yellow and orange colorings); flavoring agents (strawberry, vanilla, peach and banana essences); flavoring–coloring agents (strawberry, vanilla and peach); nisin, natamycin and lysozyme. Bacterial growth in the presence of natural fruit juices (green apple, kiwi, pineapple, peach and strawberry) with or without neutralization and cell viability in lactic acid acidified (pH 4 and 5) milk for 4 weeks at 5°C were also studied.Some compounds (KCl, sweeteners, aroma compounds, natamycin, flavoring agents and the peach flavoring–coloring agent) did not influence the growth of the strains in the concentrations commonly used in the dairy industry. The effect of other substances (especially flavoring–coloring agents) on the growth of lactic acid starters and probiotic bacteria was strain-dependent. Natural fruit juices weakly inhibited mainly S. thermophilus strains. Cell viability during cold storage in acidified milk was satisfactory for L. delbrueckii subsp. bulgaricus and L. casei group strains. For L. acidophilus and Bifidobacterium, the decreases in cell counts at pH 5 were negligible. Nevertheless, decreases from 1.6 to 6.2 and from 0.1 to 7.6 log orders, respectively were observed at pH 4.     

Survival and activity of 5 probiotic lactobacilli strains in 2 types of flavored fermented milk

The viability of 5 probiotic lactobacilli strains (Lactobacillus acidophilus LA-5, Lactobacillus casei L01, Lactobacillus casei LAFTI L26, Lactobacillus paracasei Lcp37, and Lactobacillus rhamnosus HN001) was assessed in 2 types of probiotic flavored drink based on fermented milk during 21 days of refrigerated storage (5°C). Also, changes in biochemical parameters (pH, titrable acidity, and redox potential) during fermentation as well as the sensory attributes of final product were determined. Among the probiotic strains, L. casei LAFTI L26 exhibited the highest retention of viability during refrigerated storage period, while L. acidophilus LA-5 showed the highest loss of viability during this period. The decline in cell count of probiotic bacteria in strawberry fermented milk was significantly greater compared to peach fermented milk. In an overall approach, peach fermented milk containing L. casei LAFTI L26 was selected as the optimal treatment in this study in both aspects of viability and sensory accpeptibility.     

Characterization of the angiotensin-converting enzyme inhibitory activity of fermented milks produced with Lactobacillus casei

Our study assayed angiotensin-converting enzyme (ACE) inhibitory activity and fermentation characteristics of 41 food-originated Lactobacillus casei strains in fermented milk production. Twenty-two of the tested strains produced fermented milks with a high ACE inhibitory activity of over 60%. Two strains (IMAU10408 and IMAU20411) expressing the highest ACE inhibitory activity were selected for further characterization. The heat stability (pasteurization at 63°C for 30 min, 75°C for 25 s, and 85°C for 20 s) and resistance to gastrointestinal proteases (pepsin, trypsinase, and sequential pepsin/trypsinase treatments) of the ACE inhibitory activity in the fermented milks produced with IMAU10408 and IMAU20411 were determined. Interestingly, such activity increased significantly after the heat or protease treatment. Because of the shorter milk coagulation time of L. casei IMAU20411 (vs. IMAU10408), it was selected for optimization experiments for ACE inhibitory activity production. Our results show that fermentation temperature of 37°C, inoculum density of 1 × 10⁶ cfu/g, and fermentation time of 12 h were optimal for maximizing ACE inhibitory activity. Finally, the metabolite profiles of L. casei IMAU20411 after 2 and 42 h of milk fermentation were analyzed by ultra-HPLC electron spray ionization coupled with time-of-flight mass spectrometry. Nine differential abundant metabolites were identified, and 2 of them showed a strong and positive correlation with fermented milk ACE inhibitory activity. To conclude, we have identified a novel ACE inhibitory L. casei strain, which has potential for use as a probiotic in fermented milk production.     

Short communication: Combined antimicrobial activity of reuterin and diacetyl against foodborne pathogens

Reuterin (β-hydroxypropionialdehyde) is a broad-spectrum antimicrobial substance produced by some strains of Lactobacillus reuteri during anaerobic fermentation of glycerol. Some of these strains are able to survive and produce reuterin in cheese and yogurt when added as adjuncts to the starter. Similarly, in fermented dairy foods, other inhibitory compounds such as lactic acid and diacetyl are produced during fermentation. In this work, we studied the combined effect of reuterin and diacetyl under different pH conditions against Escherichia coli O157:H7, Salmonella Enteritidis, and Listeria monocytogenes. Results from agar spot assays showed that the antimicrobial activity of reuterin-producing strains against the gram-negative bacteria tested was enhanced as the concentration of diacetyl increased to 50 mg/kg, and was higher under acidic conditions (pH 5.0) for the 3 pathogenic strains. The combination of reuterin and diacetyl had an additive effect against L. monocytogenes only at diacetyl concentrations of 50 mg/kg and pH 5.0. In addition, growth kinetics studies showed that the combination of 1 activity unit (AU)/mL of reuterin with 100 mg/kg diacetyl increased the lag time of the 3 pathogens. In milk, synergistic antimicrobial activity was observed with the combination of 1 AU/mL reuterin and 50 or 100 mg/kg of diacetyl on the gram-negative strains tested, and with 1 AU/mL reuterin and 100 mg/kg of diacetyl on L. monocytogenes. The greatest inhibition of the 3 pathogens was achieved in acidified milk at pH 5.0 with reuterin (1 AU/mL) and diacetyl (100 mg/kg). Based on these results, the combination of reuterin and diacetyl in acidified dairy products could be a promising strategy to control food pathogens in these products.     

Fermentation characteristics and transit tolerance of probiotic Lactobacillus casei Zhang in soymilk and bovine milk during storage

Lactobacillus casei Zhang is a novel strain that was screened out of koumiss collected in Inner Mongolia, and our previous research showed that L. casei Zhang has health benefits such as cholesterol-reducing and immunomodulating effects. The fermentation characteristics of L. casei Zhang in soymilk and bovine milk and the transit tolerance of L. casei Zhang in fermented milk products during refrigerated storage for 28 d were assessed. A faster decrease in pH and faster growth of L. casei Zhang during fermentation were observed in soymilk compared with bovine milk at various inoculation rates, probably because of the low pH buffering capacity of soymilk. The fermented bovine milk samples had much higher final titratable acidity (TA) values (between 0.80 and 0.93%) than the soymilk samples (between 0.40 and 0.46%). Dramatic increases in TA values in the fermented soymilk samples during storage were observed, and the TA values of the fermented soymilk samples changed from <0.56% to values between 0.86 and 0.98%. On the other hand, only slight increases in TA were observed in the bovine milk samples during the 28 d of storage. The survival rates of freshly prepared cultures of L. casei Zhang in simulated gastric juice at pH 2.0 and 2.5 were 31 and 69%, respectively, and the delivery of L. casei Zhang through fermented soymilk and bovine milk significantly improved the viability of L. casei Zhang in simulated gastric transit. Lactobacillus casei Zhang showed good tolerance to simulated gastric juice and intestinal juice in the fermented soymilk and bovine milk samples, and maintained high viability (>10⁸ cfu/g) during storage at 4°C for 28 d. Our results indicated that both soymilk and bovine milk could serve as vehicles for delivery of probiotic L. casei Zhang, and further research is needed to elucidate the mechanism of the change in pH and TA of L. casei Zhang in fermented milk samples during fermentation and storage and to understand the difference between soy- and milk-based systems.     

Effect of respirative and catalase-positive Lactobacillus casei adjuncts on the production and quality of Cheddar-type cheese

Lactobacillus casei N87 and L. casei N2014, cultivated in anaerobic and respiratory conditions, were used as adjuncts for the production of Cheddar-type cheeses. Cheese inoculated only with a defined lactococcal starter was used as control. After 14, 30, 60, 120 and 180 days of ripening, microbial counts, gross composition, proteolysis, production of volatile organic compounds, radical scavenging activity and lipid and protein oxidation were evaluated. The addition of anaerobic or respirative cultures of L. casei N87 and N2014 did not affect cheese composition and primary proteolysis. Respirative cells increased the production of free amino acids, peptides, diacetyl and acetoin and reduced the content of free radicals as well as lipid and protein oxidation. The lower redox potential in Cheddar-type cheeses produced with respirative cells also contributed to the reduction of oxidation processes. Respirative strains of L. casei could be successfully used to improve the organoleptic and nutritional properties of dairy products.     

Stimulatory effects of tea supplements on the propagation of Lactobacillus casei in milk

The influence of several Chinese teas on the ability of Lactobacillus casei to ferment milk was assessed. The three kinds of tea significantly stimulated the growth and acidification of L. casei. The viable cell counts in tea-supplemented fermented milk were higher than those of the control and were maintained during cold storage. Flavour component content increased significantly, and an additional eight components were detected in fermented milk supplemented with 5% green tea infusion (GTI_5%) compared with control fermented milk. Moreover, the increase in total free amino acids after fermentation in GTI_5% was 2.5-fold higher than in the control, suggesting that tea stimulated the growth and metabolism of L. casei during milk fermentation. Higher cell numbers, reduced fermentation time, abundant flavour components and free amino acids were achieved during the tea-supplemented fermentation of L. casei. Green tea effectively enhances the growth of L. casei, therefore could be considered for industrial purposes.     

Dissimilation of organic acids by dairy lactic acid bacteria

One hundred and eleven different strains of lactic acid bacteria, belonging to the genera Leuconostoc, Streptococcus and Lactobacillus, were examined for their ability to degrade 10 organic acids by detecting CO₂ production, using the conventional Durham tube method. All the strains did not break down succinate, glutarate, 2-oxoglutarate, or mucate. Malate, fumarate, citrate, gluconate, tartrate and pyruvate were variably attacked. A malo-lactic fermentation was brought about by two thirds of S. cremoris and S. lactis strains as well as L. casei but not by L. buchneri or L. brevis. One third of the lactic streptococci examined, i.e. S. cremoris AM₂, ML₈ and SK₁₁ were capable of diacetyl production. They required glucose for cleavage of citrate, whereas Leuconostoc citrovorum and S.faecalis did not. S. cremoris differed from S. lactis in not producing CO₂ from gluconate. From all the lactic acid bacteria examined, only L. plantarum dissimilated tartrate. Production of acetoin and diacetyl is a more reliable evidence for assessing the degradation of pyruvate, compared to detection of evolved CO₂. Facultatively heterofermentative lactobacilli and Leuconostoc citrovorum produced acetoin and diacetyl from pyruvate, whereas the obligately heterofermentative lactobacilli did not, a character that would be of taxonomic value. Glucose fermented by both the facultatively and obligately heterofermentative lactobacilli did not prove to be a metabolic source of acetoin and diacetyl. The facultative heterofermenters degraded pyruvate in the presence of glucose with lactate as the major product together with a mean of acetate of 4.1%, ethanol of 7.9%, acetoin of 1.7% and diacetyl of 2.6% yield on a molar basis after 60 days at 30°C. L. brevis produced acetate and lactate. The role of S. cremoris and the facultatively and obligately heterofermentative lactobacilli in flavour development during the ripening of many cheese varieties has been confirmed.     

The physicochemical surface characteristics of Lactobacillus casei

The surface and interfacial properties of five strains of Lactobacillus casei, commonly found in cheese, were investigated in an attempt to identify surface properties that might be exploited to effect adsorption of the cells onto milk fat globules. All measures of surface hydrophobicity revealed these strains to be moderately hydrophobic compared to a reference strain of Mycobacterium smegmatis which was very hydrophobic. In chromatography experiments, L. casei had no affinity for either hydrophobic (octyl-sepharose) or control (sepharose) columns in conditions of physiological pH and low ionic strength, despite a favorable free energy of interfacial interaction (ΔG^IF_IW2) as derived from contact angle measurements. Adhesion of L. casei strains to these materials was effected by manipulation of eluent pH and ionic strength. In contrast, adhesion of L. casei strains to n-hexadecane concurred with ΔG^IF_IW2. Surfaces of L. casei strains subjected to X-ray photoelectron spectroscopy exhibited similar amounts of carbon and oxygen but displayed considerable diversity in surface nitrogen and phosphorous contents. Carbon existed predominantly as C-(O, N) and oxygen as -OH on L. casei surfaces but carbon on M. smegmatis surfaces was present predominantly as C-(C,H).     

Effect of alpha-acetolactate decarboxylase inactivation on alpha-acetolactate and diacetyl production by Lactococcus lactis subsp. lactis biovar diacetylactis

Strains of Lactococcus lactis subsp. lactis biovar diacetylactis deficient in alpha-acetolactate decarboxylase produce alpha-acetolactate. This unstable compound is a precursor of acetoin and an aromatic compound, diacetyl. Following random mutagenesis of strain CNRZ 483, alpha-acetolactate decarboxylase-negative mutant 483 M1 was selected. When grown in milk, its growth and acidification characteristics were similar to those of the parental strain. In anaerobic conditions, the parental strain produced 2.10 mM acetoin and less than 0.05 mM diacetyl. The mutant accumulated up to 2.11 mM alpha-acetolactate, which spontaneously degraded to acetoin and diacetyl. After 24 h of culture, the alpha-acetolactate concentration was only 0.49 mM and the acetoin and diacetyl concentrations reached 1.50 mM and 0.26 mM, respectively. Diacetyl production by both strains increased in aerobic conditions, as well as when citrate was added. In contrast to cultures of the parental strain, however, diacetyl and acetoin concentrations in mutant cultures continued to increase without reaching a plateau. The results also showed that diacetyl production by wild type L. lactis subsp. lactis biovar diacetylactis strains cannot be explained uniquely by the spontaneous decarboxylation of the alpha-acetolactate produced in the culture medium.     

微生物发酵与酶法结合制备天然奶味香基的研究

选用具有丁二酮合成能力的乳酸乳球菌NRRL B-2356发酵全脂乳与脂肪酶结合制备天然奶味香基。乳酸乳球菌NRRL B-2356发酵全脂乳丁二酮、3-羟基丁酮产量在27h时达最大(52.95μg/mL),与德氏乳杆菌混合发酵,两者接种量比值为5:1时,丁二酮、3-羟基丁酮含量达60.1μg/mL,香气评分最高。利用脂肪酶palatase2000L对发酵液进行酶解修饰以提高香气强度,酸值为6.73mgKOH/g时香气评分最高。同时蒸馏萃取装置与GC-MS结合对奶味香基中挥发性成分进行了分析,结果表明,游离脂肪酸为98.586%,酮类1.219%,内酯类0.142%。研究制备的奶味香基香气纯正浓郁,可用于调配高档奶味香精。     

In vitro comparison of probiotic properties of Lactobacillus casei Zhang, a potential new probiotic, with selected probiotic strains

Since 2004, our research group has isolated 240 Lactobacillus strains from Koumiss, a traditional fermented alcoholic beverage prepared from mare's milk in Inner Mongolia, Xinjiang of China and Mongolia. Among these Lactobacillus strains a novel strain with potential probiotic properties, Lactobacillus casei Zhang, was screened out and studied extensively for its probiotic properties, health-promoting effects and fermentation characteristics. In vitro tests indicated that L. casei Zhang had high tolerance to simulated gastric, intestine juices and bile salts, similar to commercial probiotic strains such as Lactobacillus acidophilus NCFM, Lactobacillus rhamnosus GG, L. casei Shirota and Bifidobacterium animalis Bb12. Higher acid-production activity and proteolytic activity was observed in the fermented milk inoculated with L. casei Zhang during the refrigerated storage than in the samples inoculated with the selected commercial probiotics. The yogurt samples fermented with L. casei Zhang exhibited similarer viable count (1.0 × 10⁹ cfu/mL) as the other samples after 28 d of refrigerated storage. The results suggested that L. casei Zhang showed good potential for application in functional foods and health-related products.     

Two strains of nonstarter lactobacilli increased the production of flavor compounds in soft cheeses

The contribution to flavor generation and secondary proteolysis of 2 strains of mesophilic lactobacilli isolated from cheese was studied. Miniature soft cheeses (200 g) were produced with or without the inclusion of a culture of Lactobacillus plantarum I91 or Lactobacillus casei I90 in the starter composed of Streptococcus thermophilus. During ripening, cheeses containing the added lactobacilli showed an increased content of total free amino acids, but this increase was only significant in cheeses with Lb. plantarum I91. In addition, free amino acid profiles were modified by selective increases of some amino acids, such as Asp, Ser, Arg, Leu, and Phe. Cheeses inoculated with Lb. plantarum I91 or Lb. casei I90 were also characterized by a significantly higher concentration of diacetyl, a key flavor compound, and an increased content of acetoin. Results suggest an increase in the catabolism of either citrate or aspartate, with the production of the derived aroma compounds. Overall, aspartate content increased in both lactobacilli-added cheeses, whereas citrate was more or less constant, suggesting that aspartate could be the source of increased diacetyl and acetoin. A triangle aroma test showed that the addition of the lactobacilli strains significantly changed the sensory attributes of cheeses. At least 11 of 12 panelists commented that the aroma of cheeses with adjuncts was more buttery than that of control cheeses, which is desirable in most soft cheeses. Both Lb. plantarum I91 and Lb. casei I90 performed well as adjunct cultures by influencing cheese aroma development and cheese proteolysis.     

Mesopic fermentation contributes more to the formation of important flavor compounds and increased growth of Lactobacillus casei Zhang than does high temperature during milk fermentation and storage

Probiotic fermented milk is more and more popular due to their positive health associated properties. However, fermentation temperature and other process conditions may affect the growth and metabolism of probiotic strains, thereby affecting quality of the final products. In this study, the growth behaviors and metabolomic profiles of yogurts induced by Lactobacillus casei Zhang at fermentation termination (FT) and d 10 of storage (S10d) under different fermentation temperatures at 37°C (low) and 42°C (high) were analyzed and compared using liquid chromatography-mass spectrometry (MS)- and gas chromatography-MS-based metabolomics approaches. At 37°C, the growth of L. casei Zhang at FT and S10d was significantly increased, and the potential relationship between riboflavin, starch, and sucrose metabolism and growth of L. casei Zhang may be mutually promoting. Fermentation temperature (37°C and 42°C) affected volatile and nonvolatile metabolomic profiles and pathways. The levels of acetaldehyde, 2,3-butanedione, acetoin, butyric acid, decanoic acid, hexanoic acid, and octanoic acid were significantly higher at 37°C than at 42°C at FT and S10d. This indicates that the low temperature (37°C) most likely contributes more to the formation of important flavor compounds during the fermentation process and production of short-chain fatty acids during storage.     

The biological activity of fermented milk produced by Lactobacillus casei ATCC 393 during cold storage

Lactobacillus casei ATCC 393 is an important probiotic strain widely known in dairy technology. However, its capability to produce bioactive peptides from milk proteins has not been studied. The viability of the Lb. casei ATCC 393 strain and some physicochemical properties in fermented milk throughout storage for 21 days at 4 °C was evaluated; biological activity, i.e., antioxidant, angiotensin converting enzyme inhibitory and anticancer activities of water soluble extract and its filtrate (< 2 kDa; F1) were determined. Lb. casei counts remained over 9 log cfu g⁻¹ during the storage period in fermented milk. These bioactivities were increased significantly (P < 0.01) during storage. F1 of fermented milk after three weeks of storage showed the highest bioactivity impact. De novo sequencing assay for peptide identification was applied to the mass spectrum of F1. The promising capability of Lb. casei ATCC 393 to release bioactive peptides from milk proteins was demonstrated.     

Effects of the volatile organic compounds produced by Enterococcus spp. strains isolated from maize grain silos on Fusarium verticillioides growth and fumonisin B1 production

Fusarium verticillioides is a phytopathogenic fungus that can contaminate maize grain silos and result in important losses in the post-harvest product. The objective of this work was to investigate the effects of volatile organic compounds produced by four lactic acid bacterial strains isolated from maize grain silos on F. verticillioides M3125 growth and fumonisin B₁ (FB₁) production. The bacterial isolates 55 and 49 were identified as Enterococcus faecium and M4A and M4G as Enterococcus casseliflavus. The fungal growth was inhibited by 33.33% by the volatiles released by the M4A strain and by approximately 10% by the volatiles emitted by the 55 and 49 strains. The volatiles produced by the M4A strain also significantly reduced (88.75%) FB₁ biosynthesis. The gas chromatography–mass spectrometer analysis identified 21 volatile organic compounds, with diacetyl, acetic acid and acetoin being the main volatiles emitted by the four bacterial strains. Acetoin was the volatile produced in the highest proportion by the four strains, with M4A generating the highest proportion of diacetyl (35.11%). Diacetyl and acetic acid completely inhibited fungal growth at concentrations of 0.3 and 1 mM, respectively, while acetoin promoted fungal growth. Only acetoin significantly reduced FB₁ production. These results showed that diacetyl was the main compound involved in fungal inhibition, while the effect on FB₁ production could have been due to the combination of the volatile organic compounds produced by the M4A strain. In conclusion, the volatiles emitted by the E. casseliflavus M4A strain could be a promising tool for the biocontrol of F. verticillioides in storage maize grain silos.     

Citrate metabolism in Lactococcus lactis subsp. lactis var. diacetylactis strains

The formation of diacetyl, acetoin, 2,3-butylene glycol, acetaldehyde, ethanol and lactic acid during 24 h of cultivation in milk with 0.19 and 0.5 % of citrate has been studied. Depending on the strain, bacteria produced 1.5 - 1.9 mg of diacetyl, 212 - 311 mg of acetoin and 137 - 156 mg of butylene glycol in 1 1 milk. An increase of the citrate concentration in milk to 0.5 % resulted in an increase in the production of diacetyl from 58 to 74 % and of acetoin by 2.8 - 3.7 times. The strains of distinct activity of acetoin reductase produced in these conditions 2.3 - 2.7 times as much as 2,3-butylene glycol. The recovery of citrate in the from of C₄-compounds ranged from 76 to 98 %, yet barely 0.18 - 0.44 % in the from of diacetyl. Increased concentration of citrate in milk stimulated the production of diacetyl and acetaldehyde to the similar extent, thereby it did not result in the deterioration of organoleptic qualities of starters and milk products. Within the doses used citrate did not significantly affect growth and acidifying activity of the bacteria.     

Survival of probiotic lactobacilli in the upper gastrointestinal tract using an in vitro gastric model of digestion

The aim of this study was to investigate survival of three commercial probiotic strains (Lactobacillus casei subsp. shirota, L. casei subsp. immunitas, Lactobacillus acidophilus subsp. johnsonii) in the human upper gastrointestinal (GI) tract using a dynamic gastric model (DGM) of digestion followed by incubation under duodenal conditions. Water and milk were used as food matrices and survival was evaluated in both logarithmic and stationary phase. The % of recovery in logarithmic phase ranged from 1.0% to 43.8% in water for all tested strains, and from 80.5% to 197% in milk. Higher survival was observed in stationary phase for all strains. L. acidophilus subsp. johnsonii showed the highest survival rate in both water (93.9%) and milk (202.4%). Lactic acid production was higher in stationary phase, L. casei subsp. shirota producing the highest concentration (98.2 mM) after in vitro gastric plus duodenal digestion.     

Influence of cofermentation by amylolytic Lactobacillus strains and probiotic bacteria on the fermentation process,viscosity and microstructure of gruels made of rice,soy milk and passion fruit fiber

Gruels tailored to school-age children and made of soy milk and rice flour with or without total dietary fiber from passion fruit by-product were fermented by amylolytic lactic acid bacteria strains (Lactobacillus fermentum Ogi E1 and Lactobacillus plantarum A6), by commercial probiotic bacteria strains (Lactobacillus acidophilus L10, Lactobacillus casei L26 and Bifidobacterium animalis subsp. lactis B94) and by co-cultures made of one amylolytic and one probiotic strain. The influence of ingredient composition and bacterial cultures on kinetics of acidification, α-amylase activity of the bacteria, apparent viscosity and microstructure of the fermented products was investigated. During fermentation of the gruels, α-amylase activity was determined through the Ceralpha method and apparent viscosity, flux behavior and thixotropy were determined in a rotational viscometer. Rheological data were fitted to Power Law model. The combination of amylolytic and probiotic bacteria strains reduced the fermentation time of the gruels as well as increased the α-amylase activity. The addition of passion fruit fiber exerted less influence on the apparent viscosity of the fermented products than the composition of the bacterial cultures. Scanning electron microscopy provided evidence of exopolysaccharide production by amylolytic bacteria strains in the food matrices tested. The co-cultures made of amylolytic and probiotic bacteria strains are suitable to reduce the fermentation time of a soy milk/rice matrix and to obtain a final product with pH and viscosity similar to yoghurt.