Starter Concentration Research Articles

EXPERIMENTAL VACUUM SPRAY DRYING OF PROBIOTIC FOODS INCLUDED WITH LACTIC ACID BACTERIA

ABSTRACT This research aims to develop a vacuum spray dryer (VSD) that performs spray drying in a vacuumed drying tower at a lower temperature than the conventional spray drying. The VSD operational drying temperatures for the probiotic foods containing lactic acid bacteria were determined by the relationships between the temperature and the vapor pressure, and were correlated by Clapeyron's equation. The drying of the fermented milk starter at 35C drying tower was experimentally possible; however, powder from the lactic fermenting beverage was not obtained even at 50C, which resulted from the lower glass transition temperature of the material. Compared with ATP concentration of the fermented milk starter before and after the VSD drying, the lower the drying temperature, the higher the microbial activity is retained. The ATP ratio as 30% of the raw materials shows the high feasibility of VSD for dairy processing. PRACTICAL APPLICATIONS During the spray drying of liquid or slurry food, the heat-sensitive functional ingredients such as vitamin, enzyme or bacteria are usually degraded or lost because of the contact with hot air between 120 and 180C. Markets need food powder that involves a lot of functional materials and a long shelf life for the expansion of healthy food. The experimental vacuum spray dryer (VSD) showed a potential to dry probiotic foods involving lactic acid bacteria without their inactivation. Although the lactic acid bacteria contained in the powder at 35C–VSD was 30% of the raw material, it is more economical than using the liquid type fermented milk starter. With some mechanical or operational modifications for the high moisture content and low recovery ratio of the powder, VSD is applicable for dairy processing factories.

Low energy Kombucha fermented milk-based beverages

This paper investigates manufacturing of fermented beverages from two types of milk (1 % w/w and 2.2 % w/w fat) by applying of Kombucha, which contains several yeasts and bacterial strains. The starter was the inoculum produced from previous Kombucha fermentation. The applied starter concentrations were: 10 % v/v, 15 % v/v and 20 % v/v. Also, the traditional yoghurt starter was used to produce the control samples. All fermentations were performed at 42oC and the changes in the pH were monitored. The fermentation process was about three times faster in the control yoghurt than in the Kombucha samples. Influence of Kombucha inoculum concentration on the rate of fermentation appeared not to be significant. All fermentations were stopped when the pH reached 4.4. After the production, the quality of the fermented milk beverages with Kombucha was determined and compared with the quality of the control yoghurt samples. It was concluded that the difference in fat contents in milks affects the difference in quantities of other components in the fermented milk beverages with Kombucha. Sensory characteristics of the beverages manufactured from the partially skimmed milk are much better than those of the fermented beverages produced from the low fat milk.

Monitoring the Chemical and Textural Changes During Ripening of Iranian White Cheese Made with Different Concentrations of Starter

The effect of the concentration of starter inoculated to milk on the composition, free tyrosine-tryptophan content, microstructure, opacity, and fracture stress of Iranian White cheese (IWC) was studied during 50 d of ripening in brine. Three treatments of cheese were made using 1-fold (IWC1S), 2-fold (IWC2S), and 4-fold (IWC4S) concentrations of a direct-to-vat mesophilic mixed culture containing Lactococcus lactis ssp. cremoris and Lactococcus lactis ssp. lactis as starter. As ripening progressed, moisture and protein contents of the treatments continuously decreased, whereas their total ash, salt, and salt in moisture contents increased. Fat content and pH of cheeses remained stable during ripening. The pH of cheese milk at the time of renneting, which decreased by increasing the concentration of starter (6.57, 6.49, and 6.29 for IWC1S, IWC2S, and IWC4S, respectively), significantly affected most of the chemical characteristics and opacity of cheese. Lower pH values at renneting decreased moisture and ash contents, whereas cheese protein content increased. The concentration of free tyrosine-tryptophan in curd increased at first 29 d but decreased between d 29 and 49 of aging. The changes observed in cheese whiteness followed the changes in moisture content of the treatments. As the concentration of starter inoculated to milk increased, the value of fracture stress at a given ripening time significantly decreased, leading to a less resistant body against applied stress. A similar trend was also observed for fracture strain during cheese ripening. The micrographs taken by scanning electron microscopy provided a meaningful explanation for decrease in the value of fracture stress. As the cheese ripening progressed or the concentration of starter increased, the surface area occupied by the protein fraction in cheese microstructure decreased, leading the way to lower the force-bearing component in cheese texture.

Characterization of the tre Locus and Analysis of Trehalose Cryoprotection in Lactobacillus acidophilus NCFM

Freezing and lyophilization are common methods used for preservation and storage of microorganisms during the production of concentrated starter cultures destined for industrial fermentations or product formulations. The compatible solute trehalose has been widely reported to protect bacterial, yeast and animal cells against a variety of environmental stresses, particularly freezing and dehydration. Analysis of the Lactobacillus acidophilus NCFM genome revealed a putative trehalose utilization locus consisting of a transcriptional regulator, treR; a trehalose phosphoenolpyruvate transferase system (PTS) transporter, treB; and a trehalose-6-phosphate hydrolase, treC. The objective of this study was to characterize the tre locus in L. acidophilus and determine whether or not intracellular uptake of trehalose contributes to cryoprotection. Cells subjected to repeated freezing and thawing cycles were monitored for survival in the presence of various concentrations of trehalose. At 20% trehalose a 2-log increase in survival was observed. The trehalose PTS transporter and trehalose hydrolase were disrupted by targeted plasmid insertions. The resulting mutants were unable to grow on trehalose, indicating that both trehalose transport into the cell via a PTS and hydrolysis via a trehalose-6-phosphate hydrolase were necessary for trehalose fermentation. Trehalose uptake was found to be significantly reduced in the transporter mutant but unaffected in the hydrolase mutant. Additionally, the cryoprotective effect of trehalose was reduced in these mutants, suggesting that intracellular transport and hydrolysis contribute significantly to cryoprotection.

Development of food grade media for the preparation of Lactobacillus plantarum starter culture

Based on MRS medium, two types of food grade (FG) culture media (FG medium I and FG medium II) for the preparation of a concentrated starter culture of Lactobacillus plantarum NRIC 0380 to manufacture a new type of instant Chinese noodle, the fermented instant Chinese noodle, were developed using FG materials. FG medium I, which is for normal static culture, contains table sugar (sucrose), Yeast peptone standard type F, Sunsoft Q-17S (emulsifier), sodium acetate, trisodium citrate and MnSO(4).4-5H(2)O. FG medium II was designed to be used for the pH-controlled jar fermentor culture conditions. Therefore, sodium acetate and trisodium citrate as a buffer to prevent acidification of medium were omitted from FG medium I. When L. plantarum NRIC 0380 was cultured under the pH-controlled jar fermentor culture conditions, the kinetics of growth, sugar consumption and lactic acid production in FG medium II were quite similar to those observed in the Difco Lactobacilli MRS Broth. Furthermore, growths of many lactobacilli strains isolated from various fermented foods in FG medium I were also quite similar to those observed in MRS medium. Therefore, simple and practical FG media for the culture of lactobacilli were successfully established.

The effect of temperature and inoculum concentration on rheological and light scatter properties of milk coagulated by a combination of bacterial fermentation and chymosin. Cottage cheese-type gels

The main differences between the processing methods generally used for cottage cheese manufacture are the coagulation temperature and starter concentration. The effects of these factors on cottage cheese gels were investigated. Gels were made with a low rennet concentration. Gel formation was monitored using infrared light backscatter and dynamic small amplitude oscillatory rheology. Light backscatter profile was explained by a complex combination of casein micelle aggregation, curd firming and micelle demineralization. Increasing temperature or inoculum concentration resulted in faster network formation, which resulted in more viscous and less stiff gels. Activation energy of aggregation decreased significantly with increasing starter concentration. Casein aggregation had a higher temperature coefficient than firming and transition from rennet- to acid-type gels mostly occurred during curd firming stage of network formation. The second minimum of the backscatter profile second derivative and the rheological gelation time were highly correlated but not significantly different, suggesting that they both corresponded to the beginning of gel firming.

Effects of the Starter Diet, Light Intensity, and Essential Amino Acids Level on Growth and Carcass Composition of Broilers

Optimal return in broiler production requires a better understanding of interactions between nutrition at different ages and environmental factors. In the present experiment, the effect of the starter diet on subsequent response of male broilers to increasing levels of essential amino acids (EAA) in their diet (85, 95, 105, and 115% of NRC) from 21 to 42 d of age were evaluated under 2 light intensities (80 and 5 lx). Results confirmed that EAA requirement of finishing broilers might be higher than 115% of the recommendation of the NRC. Light intensity did not interact significantly with the nutritional factors. A more concentrated starter diet persistently stimulated growth and breast development but might reduce the resistance of broilers to stresses. Early nutrition of broiler chicks requires further research.

Effect of initial glucose concentration and inoculation level of lactic acid bacteria in shrimp waste ensilation.

Fermentation conditions and microorganisms were determined, based on acid production, glucose concentration as carbohydrate source. Inoculation levels to obtain a stable shrimp waste silage were also determined. Shrimp waste ensilation was an efficient method of preservation, allowing the recovery of chitin and another added-value products such as pigments, proteins and enzymes. From the various lactic acid bacteria tested, Lactobacillus pentosus and Lactobacillus sp. (B2) were the best lactic acid producers, although small quantities of acetic acid were detected in samples inoculated with Lactobacillus pentosus. Therefore B2 was chosen for the analysis of glucose consumption as well as for the determination of optimum inoculation levels. The best results were obtained at 10% (w/w wet basis) and 5% (v/w wet basis) respectively. Presence of starters and initial glucose concentration were critical factors in the fermentation of shrimp waste. High initial glucose and starter concentrations reduced the time and increased the amount of lactic acid produced. The fermentation pattern changed during ensilation from hetero to homofermentative. Shrimp waste ensilation prevented the growth of spoilage microorganisms keeping their microbial counts steady and pH values within the acid region.

Combined effects of concentrated thermophilic and mesophilic cultures and conditions of curd acidifications on the manufacture and quality of kasseri cheese

The effect offour process variables on the biological acidification of curd to be usedfor the manufacture of kasseri cheese was examined. The variables were (i) concentrated starter cultures: a thermophilic mixture of Streptococcus thermophilus and Lactobacillus delbrueckii subsp bulgar‐icus compared with a blend of Lactococcus lactis subsp lactis, Lactococcus lactis subsp cremoris and Lactobacillus casei subsp casei, and (ii) acidification temperatures: 30 and 40° C for the thermophilic cultures and 20 and 30°C for the mesophiles. The use of concentrated starter cultures enabled the cheese to be made in one day as compared with three in the traditional system usually using raw milk and no culture. The mesophilic blend combined with a lower scalding temperature (35°C) gave a higher yield than the alternative culture, and the cheeses were higher in total solids, acidity andsalt; the same cheeses were also harder and less elastic. The use of mesophilic cultures and a low acidification temperature (20° C) is recommended.

Mid-Infrared Spectroscopic Determination of Sugar Contents in Culture Media

A simple, rapid and accurate method for determining sugar contents in culture media by mid-infrared spectroscopy was developed using a Fourier transform infrared spectrometer equipped with an attenuated total reflectance accessory by focusing our attention on sugar consumption by plant cells. In addition, we performed lactic acid fermentation under the different conditions of the media and the starter concentration to examine this measuring method. Consequently, this study represents an important step in the development of nonintensive on-line monitoring devices for bioreactors and of simple, rapid and accurate analysis of the cellular metabolism through the composition changes in media.

Ultrafiltered Gouda Cheese: Effects of Preacidification, Diafiltration, Rennet and Starter Concentration, and Time to Cut

The effects of cheese milk preacidification pH, percentage of diafiltration water added during UF, rennet concentration, starter culture concentration, and time between coagulation and cut on the composition and ripening of Gouda cheese made from ultrafiltered milk were evaluated. Preacidification of cheese milk to pH 6.3 resulted in some decrease in cheese pH, which is desirable because the cheeses made from ultrafiltered milk produced in this study often had pH values above that of conventional cheese. Diafiltration level appears to be important because a low diafiltration level led to decreased cheese ripening measured as phosphotungstic acid- and TCA-soluble N. In this study, a decreased rennet concentration (one-third of conventional cheese) was found to be optimal because a level of two-thirds of conventional cheese led to excessive bitterness. Also, in this study, starter (3%), based on the weight of the retentate, gave a cheese pH and moisture more similar to the conventional cheese. On a volume basis, this amount of starter is less than that used for the conventional cheese. Increasing time between coagulation and cut did not noticeably improve texture.

Production of concentratedStreptococcus salivariussubsp.thermophilusby coupling continuous fermentation and ultrafiltration

SummaryContinuous production of concentrated cells ofStreptococcus salivariussubsp.thermophiluswas achieved in a continuous stirred tank reactor coupled with an ultrafiltration module. A cellular productivity nine times higher than that obtained by conventional methods was observed. The viability of the cells produced was as satisfactory as that obtained by classical culture, but an increase in latency time and a slight decrease in acidification rate during downstream tests in milk were observed. Specific lactic acid productivity decreased as biomass increased. This process produced concentrated starters and lactic acid which could be purified by a downstream processing such as electrodialysis.

Antioxidants and storage atmospheres for freeze-dried concentrated starters from non-bitterStreptococcus lactis strains

The highest viability and acid-producing activity of freeze-dried concentrated starters prepared from non-bitterStreptococcus lactis strains after storage at 4 or 20 C for 60 days were consistently achieved by the use of ascorbic acid + monosodium glutamate as antioxidant and of N2 as storage atmosphere.

Cryoprotective agents for frozen concentrated starters from non-bitterStreptococcus lactis strains

Six cryoprotective agents were tested on cells harvested from 4 pH-regulated fermentations of a non-bitterS. lactis strain. Addition of 5% lactose or 5% sucrose to centrifugation pellets and a storage temperature of −40 C or −70 C resulted in the highest viability and acid-producing activity of frozen concentrated starters.

Growth and enterotoxin A production by Staphylococcus aureus S6 in Manchego type cheese.

Milk (from cow, goat and sheep) was inoculated with Staphylococcus aureus strain S6, which is generally considered to be a strong enterotoxin B producer and a weak enterotoxin A producer. It was then used to make Manchego type cheese as prepared industrially. Two concentrations of starter culture (1% and 0.1%) were tested. Staphylococcal growth was good in both but better in the more dilute culture. Staphylococcal enterotoxin B was not detected at any stage of the ripening process of any cheese tested. However enterotoxin A was detected in both starter concentrations, reaching as high as 769 ng/100 g of cheese in the 0.1% starter batches.

Application of Retentate Starter Produced from Ultrafiltered Milk to the Manufacture of Cheddar Cheese

Cheddar cheese was manufactured from whole milk and whole milk retentate using retentate starter made from milk ultrafiltered to 4:1 (vol/vol). One percent retentate starter added to whole milk and 2% starter to 1.7:1 whole milk retentate gave excellent quality cheese. Additionally, a 1% retentate starter added to whole milk gave approximately 3% more cheese. A 2% retentate starter added to 1.7:1 whole milk retentate gave 4% more cheese, reduced cheese making time over that required for control whole milk cheese, and made acid ripening of milk before renneting unnecessary. Starter concentrations above 1% in whole milk and above 2% in whole milk retentates produced some bitterness in the cheese.

Inhibition of Enteropathogenic Escherichia coli by Homofermentative Lactic Acid Bacteria in Skimmilk

Behavior of enteropathogenic and nonpathogenic strains of Escherichia coli was determined when they were grown in skimmilk with and without 0.25 or 2.0% added lactic starter and incubated at 21 or 32 C for 15 h, and then after refrigeration at 7 C. With no lactics present, generation times for E. coli ranged from 28 to 35 min at 32 C and from 66 to 109 min at 21 C. At 32 C, after an initial 1- to 3-log increase in numbers and 6 to 9 h of incubation, E. coli was completely inhibited by both concentrations of starter culture. Complete inhibition of growth by E. coli occurred earlier at 32 than at 21 C, but smaller numbers of E. coli were obtained at 21 C; some strains virtually did not grow. The final pH of fermented milks ranged from 4.4 to 4.6. The longest survival time for E. coli in refrigerated fermented milk was about 17 days when milk was fermented at 32 C with 0.25% starter. A combination of lower incubation temperature (21 C) and higher starter concentration (2.0%) was most effective in controlling growth of E. coli in fermented skimmilk.

Effects of variation in dietary energy concentration of starter and finisher diets on broiler production

Least-cost starter and finisher broiler diets at five levels of metabolizable energy (ME) concentration were formulated. The diets were fed in selected combinations of starter and finisher energy concentration to batches of broiler chickens to 1650 g. Performance data were recorded and it was found that best biological efficiency was obtained by feeding starter-finisher diets with ME concentrations in the range 12.6 to 13.8 MJ kg-1. However, best economic results were obtained from diets with energy concentrations somewhat below these levels, at approximately 12.2 to 12.5 MJ kg-1. There was no evidence that ME of the starter diet influenced the ME concentration of the finisher diet required for optimal performance.

MANUFACTURE OF STARTERS: PRODUCTION OF FROZEN CONCENTRATED CHEESE STARTERS BY DIFFUSION CULTURE

Diffusion culture allows the production of concentrated cheese starter without centrifugation principally by removing inhibitory lactate from fermentations. Laboratory scale fermentation systems are described which remove lactate via a diffusion membrane. Single and mixed strain cultures were grown to concentrations of 1011/ml in an enzyme digest of skimmed milk supplemented with yeast extract. The present stage system is capable of producing at least half the annual bulk starter requirements of a creamery processing 100,000 gal of milk/day. Concentrated cultures were harvested in hypodermic syringes and as frozen granules. Concentrates were tested for purity and activity and suitable ones used in a commercial cheesemaking trial which produced a high proportion of extra selected grade Cheddar cheese.

MANUFACTURE OF STARTERS: THE USE OF COMMERCIALLY AVAILABLE CONCENTRATED STARTERS

The paper describes the starters available from the author's company for use in the manufacture of various fermented dairy products. These starters are normally supplied as deep frozen concentrates and are divided into two groups with appropriate sub groups according to the type of product. As expected cheese gives rise to a wide variety of cultures because of their use in many countries. Except for products produced in small quantity, these deep frozen concentrated starters are not used by direct inoculation into the requisite volume of heat treated milk but are used to produce bulk starter. Recommendations for usage with underlying reasons are also dealt with.