Influence of water activity on the fermentation of yogurt made with extracellular polysaccharide-producing or non-producing starters

Comparison of Physical and Compositional Attributes between Commercial Plant-Based and Dairy Yogurts

A primary strategy led by the food industry to improve the sustainability of the agricultural food supply is the development of modern plant-based alternatives. The information provided via marketing and product packaging provides consumers with the expectation that these products provide a similar product experience to conventional products, yet it is not well understood whether these commercial alternative products are comparable to traditional animal-based products. To aid in developing improved plant-based products, this study aimed to compare the quality and physical attributes of commercially available plant-based and dairy yogurts. Using instrumental methods, commercially available yogurt products were analyzed for their pH, titratable acidity, color, water activity, moisture content, and rheology, which included 13 plant-based (almond, cashew, coconut, oat, soy) and 8 whole-milk dairy yogurts. The present study reveals that the plant-based and dairy yogurts had no significant differences in pH, lactic acid, water activity, or moisture content. However, there were significant differences in the color and texture properties between the plant-based and dairy yogurts. Additionally, significant differences were observed across the plant-based yogurt products in terms of their color and texture properties. This highlights the need for additional studies to determine how individual ingredients influence the physical characteristics and textural properties to direct the development of plant-based yogurts. Improving upon the physicochemical properties of plant-based yogurt may encourage more consumers to adopt a more sustainable diet.

Effect of flaxseed oil and flour on sensory, physicochemical and fatty acid profile of the fruit yoghurt

The objective of this study was to incorporate flaxseed oil, flaxseed flour and fruits for the preparation of fruit yoghurt and analysed for their sensory, physicochemical and fatty acid profile. Overall acceptability of sensory scores indicates that fruit yoghurt (20% fruit and sugar mixture) with incorporation of flaxseed oil up to 2% and flaxseed flour up to 1% in combination can be used for preparation of fruit yoghurt with acceptable sensory attributes. The scores drastically reduced for yoghurt samples wherein 2% flaxseed flour was incorporated. The mixture of sugar and fruits diluted the milk composition and resulted in lower values in the fruit yoghurts. The increase in fat, protein, carbohydrate, minerals content in the yoghurt was mainly contributed by the flaxseed oil and flour. The addition of flaxseed oil did not show any affect on the water activity of the yoghurt samples. The yoghurt had dietary fiber content of 1.24%. The fresh control fruit yoghurt showed the acidity value of 0.88% LA, while the corresponding value for experimental samples varied between 0.85 and 0.88% LA. TBA values increased with increased incorporation of flaxseed oil and flaxseed flour. The fatty acid analysis revealed that alpha linolenic acid (ALA) content increased from 0.45% of ALA in control sample to 22.80% of ALA in the final product.

Environmental factors influencing growth of and exopolysaccharide formation by Pediococcus parvulus 2.6

Natural exopolysaccharides (EPSs) from food-grade lactic acid bacteria have potential for development and exploitation as food additives and functional food ingredients with both health and economic benefits. In this study, we have examined the physiological capacity of EPS production in Pediococcus parvulus 2.6. EPS formation by P. parvulus 2.6 was found to be linked to biomass yields, provided that glucose was not limiting. Higher biomass yields and EPS productions were obtained when cultures were pH-controlled at pH 5.2. Various compounds have been tested for their influence on growth rate and EPS formation. Of those, only glucose (up to 75 g l(-1)), ethanol (up to 4.9%, w/v) and glycerol (up to 6.6%, w/v) had positive effects on EPS production. EPS production was not directly linked to growth, because its production continued in the stationary phase provided that glucose was present. According to an empirical model, the growth of P. parvulus 2.6 was completely inhibited by 58.9+/-18.1 g l(-1) lactate. Lactate, the sole fermentation product, was suggested to affect growth by chelation of manganese. The organism grew in an apparent linear fashion due to this imposed manganese limitation. This could be overcome by increasing the manganese concentration to at least 2 mg l(-1) in the medium. The excretion of Mn(2+) upon depletion of glucose indicated that maintenance of the high Mn(2+) gradient over the cell membrane is an energy requiring process. EPS production was increased from 0.12 g l(-1) to 4.10 g l(-1) in an improved medium that is based on the results from this study.

Growth and exopolysaccharide production by Lactobacillus helveticus ATCC 15807 in an adenine-supplemented chemically defined medium

AIMS

To analyse the exopolysaccharide (EPS) production by Lactobacillus helveticus ATCC 15807 in a chemically defined medium (CDM) and the effect of nutrients and stress culture conditions on cell growth and EPS formation.

METHODS AND RESULTS

Cultures were conducted in CDM: (i) containing essential and nonessential bases and vitamins; (ii) without nonessential bases and vitamins [Simplified CDM (SCDM)]; (iii) SCDM supplemented individually with vitamins and bases. The influence of carbohydrates, pH and osmotic culture conditions on growth and polymer formation was analysed. Adenine and lactose stimulated both growth and EPS production. Constant pH fermentations (4.5 and 6.2) did not improve EPS synthesis while NaCl and glycerol were detrimental for growth and polymer formation. In all media the EPS monomer composition was glucose and galactose (2.5 : 1).

CONCLUSIONS

A SCDM containing adenine and lactose was optimal for cell growth and EPS formation by Lact. helveticus ATCC 15807. Controlled pH (6.2 and 4.5) and osmotic stress culture conditions did not improve polymer production. The EPS characteristics were identical in all media.

SIGNIFICANCE AND IMPACT OF THE STUDY

This work provides a better knowledge on EPS synthesis by Lact. helveticus. A CDM to perform regulation studies on EPS production by Lact. helveticus species is now available.

Physiological function of exopolysaccharides produced by Lactococcus lactis

The physiological function of EPS produced by Lactococcus lactis was studied by comparing the tolerance of the non-EPS producing strain L. lactis ssp. cremoris MG1614 and an EPS producing isogenic variant of this strain to several anti-microbial factors. There was no difference in the sensitivity of the strains to increased temperatures, freezing or freeze-drying and the antibiotics, penicillin and vancomycin. A model system showed that EPS production did not affect the survival of L. lactis during passage through the gastrointestinal tract although the EPS itself was not degraded during this passage. The presence of cell associated EPS and EPS in suspension resulted in an increased tolerance to copper and nisin. Furthermore, cell associated EPS also protected the bacteria against bacteriophages and the cell wall degrading enzyme lysozyme. However, it has not been possible, so far, to increase EPS production using the presence of copper, nisin, lysozyme or bacteriophages as inducing factors.