L. Gómez-Ruiz

Evaluation of Kluyveromyces marxianus as baker's yeast

Abstract Two strains of Kluyveromyces marxianus (NRRL-Y-2415 and NRRL-Y-1109) were assessed as bakers yeasts comparing them with two strains of Saccharomyces cerevisiae isolated respectively from compressed yeast and active dry yeast. Strains were tested for dough proofing activity in lean dough and rich doughs (prepared with sucrose, lactose or whey) and sensory evaluation of breads. In rich doughs containing lactose or whey, both strains of K. marxianus had superior proofing activity compared to commercial bakers yeast strains but no difference in bread flavor was detected.

Isolation and identification of killer yeasts from Agave sap ( aguamiel) and pulque

Wild killer yeasts have been identified as inhibitory to strains used as starters in the production of alcoholic beverages such as beer and wine; therefore, killer or killer-resistant strains have been sought for use in alcoholic fermentations. In the current paper a total of 16 strains belonging to six species were isolated. From two samples of Agave sap (aguamiel) the following yeast strains were isolated: Candida lusitaneae (1), Kluyveromyces marxianus var. bulgaricus (2), and Saccharomyces cerevisiae (capensis) (1). Additionally, in seven samples of pulque (the fermented product), the species C. valida (six strains), S. cerevisiae (chevalieri) (4), S. cerevisiae (capensis) (1), and K. marxianus var. lactis (1) were found. The killer strains were C. valida and K. marxianus var. lactis from pulque and K. marxianus var. bulgaricus from aguamiel. One strain of S. cerevisiae (chevalieri) isolated from pulque which did not show killer activity was, on the other hand, resistant to other killer strains and it had a remarkable ethanol tolerance, suggesting that this strain could be used for alcohol production.

Isolation and identification of killer yeasts from sugar cane molasses

A total of 13 yeast strains were isolated from 10 samples of sugar cane molasses obtained from sugar mills in Mexico; nine of them were killer strains. There was at least one killer strain in every sample. The resulting species were the following: Torulaspora delbrueckii (2), Schizosaccharomyces pombe (7), Cryptococcus albidus var. albidus (1) and Saccharomyces cerevisiae (3). A new killer species is reported: Schizosaccharomyces pombe.

Dissolved oxygen threshold for the repression of endo-polygalacturonase production by Kluyveromyces marxianus

Abstract A detailed study was conducted in terms of the influence of dissolved oxygen (DO) and growth temperature related to the endo-polygalacturonase synthesis by the yeast Kluyveromyces marxianus CDBB-L-278. It was found that 3.3 mg of DO/l was the threshold for the repression of enzyme production. Growth temperature had no effect on the synthesis of this enzyme, but had an indirect effect due to changes in oxygen solubility. Growth rate was influenced by temperature; maintaining the dissolved oxygen constant at 3.3 mg of DO/l, the optimum growth temperature was 40°C. Pectin in the culture medium allowed higher endo-polygalacturonase production; even with 3.3 mg of DO/l, pectin de-repressed the enzyme production.

Commercial probiotic bacteria and prebiotic carbohydrates: a fundamental study on prebiotics uptake, antimicrobials production and inhibition of pathogens.

BACKGROUND Probiotics and prebiotics are among the most important functional food ingredients worldwide. The proven benefits of such ingredients to human health have encouraged the development of functional foods containing both probiotics and prebiotics. In this work, the production of antimicrobial compounds coupled to the uptake of commercial prebiotics by probiotic bacteria was investigated. RESULTS The probiotic bacteria studied were able to take up commercial prebiotic carbohydrates to the same or higher extent than that observed for lactose (control carbohydrate). The growth of probiotic bacteria was coupled to the production of antimicrobials such as short-chain fatty acids (SCFA), H2 O2 and bacteriocins. A higher production of antimicrobial compounds was recorded with Oligomate 55® compared with Regulact® and Frutafit® (3-5 and 10-115 times higher SCFA and H2 O2 production, respectively). The probiotic bacteria grown with Oligomate 55® also produced bacteriocins and other non-identified antimicrobial compounds. The antimicrobials produced by the probiotic bacteria inhibited up to 50% the growth of model pathogens such as Escherichia coli, Listeria innocua and Micrococcus luteus compared with control cultures. CONCLUSIONS The results here obtained are useful for the adequate selection of probiotic/prebiotics pairs and therefore in the development of efficient functional foods.

Degradation of α-Lactalbumin and β-Lactoglobulin by Actinidin

Susceptibility of the two major whey proteins, β-lactoglobulin and α-lactalbumin, to enzymatic degradation by actinidin as a function of pH and temperature was examined by a response surface methodology in order to elucidate the enzymatic action of the protease for controlled modification of these whey proteins. Pure whey protein fractions and commercial spray-dried whey were degraded by actinidin. The simultaneous effects of pH and temperature, in a range of 2.3 to 5 and 41 to 58°C respectively, on whey proteins degradation were studied, demonstrating a clear interrelationship between these two variables. With commercial whey, extended proteolysis of both β-lactoglobulin and α-lactalbumin was observed at pH 4.0 and temperature of 41.6°C; after an incubation time of 120 min, a degradation of 43.6% was obtained for the former, and 89.1% for the latter. Assays on pure proteins showed a complete degradation of α-lactalbumin and a 65.3% of degradation for β-lactoglobulin; therefore, the former appeared to be more susceptible to actinidin proteolysis.

SINGLE CELL PROTEIN | Yeasts and Bacteria

Yeasts and bacteria have been particularly important for single-cell protein (SCP) production; they represent the most widely used microorganisms for this purpose: the former mainly for human consumption and the latter frequently used for feed production. Substrates for yeast and bacteria biomass growth include food-processing by-products as well as fossil hydrocarbons. Yeasts have been the preferred source for SCP production over bacteria, particularly for human consumption, as they are related to products, such as bread or beer; however, bacteria have higher protein content, higher yields, and faster growth rate, but they are less accepted for human food. The main drawback for the SCP consumption is its high content of nucleic acids and components of cell wall, which limits its uptake in the diet, at least so that the biomass can be processed to isolate the protein.

SINGLE-CELL PROTEIN | The Algae

Algae, as source of single-cell protein (SCP), is a term that refers to either microscopic single-cell true algae or prokaryotic cyanobacteria, and their growth is based on the use of carbon dioxide and light energy (autotrophic growth). In contrast with other SCP-producing organisms, algae are grown in many cases by processes resembling traditional agriculture, because they depend on large areas and sunlight radiation; on the other hand, modern production techniques include growth inside photobioreactors. Moreover, macroscopic algae are used widely as source of food, but they hardly can fit the SCP definition because of their multicellular nature and low protein content.