Isolation of an l-methionine-enriched mutant of Kluyveromyces lactis grown on whey permeate

Cheese whey: A potential resource to transform into bioprotein, functional/nutritional proteins and bioactive peptides

The byproduct of cheese-producing industries, cheese whey, is considered as an environmental pollutant due to its high BOD and COD concentrations. The high organic load of whey arises from the presence of residual milk nutrients. As demand for milk-derived products is increasing, it leads to increased production of whey, which poses a serious management problem. To overcome this problem, various technological approaches have been employed to convert whey into value-added products. These technological advancements have enhanced whey utilization and about 50% of the total produced whey is now transformed into value-added products such as whey powder, whey protein, whey permeate, bioethanol, biopolymers, hydrogen, methane, electricity bioprotein (single cell protein) and probiotics. Among various value-added products, the transformation of whey into proteinaceous products is attractive and demanding. The main important factor which is attractive for transformation of whey into proteinaceous products is the generally recognized as safe (GRAS) regulatory status of whey. Whey and whey permeate are biotransformed into proteinaceous feed and food-grade bioprotein/single cell protein through fermentation. On the other hand, whey can be directly processed to obtain whey protein concentrate, whey protein isolate, and individual whey proteins. Further, whey proteins are also transformed into bioactive peptides via enzymatic or fermentation processes. The proteinaceous products have applications as functional, nutritional and therapeutic commodities. Whey characteristics, and its transformation processes for proteinaceous products such as bioproteins, functional/nutritional protein and bioactive peptides are covered in this review.

Characterization of isolated yeast growth response to methionine analogs

Methionine is one of the first limiting amino acids in poultry nutrition. The use of methionine-rich natural feed ingredients, such as soybean meal or rapeseed meal may lead to negative environmental consequences. Amino acid supplementation leads to reduced use of protein-rich ingredients. The objectives of this study were isolation of potentially high content methionine-containing yeasts, quantification of methionine content in yeasts and their respective growth response to methionine analogs. Minimal medium was used as the selection medium and the isolation medium of methionine-producing yeasts from yeast collection and environmental samples, respectively. Two yeasts previously collected along with six additional strains isolated from Caucasian kefir grains, air-trapped, cantaloupe, and three soil samples could grow on minimal medium. Only two of the newly isolated strains, K1 and C1, grew in minimal medium supplied with either methionine analogs ethionine or norleucine at 0.5% (w/v). Based on large subunit rRNA sequences, these isolated strains were identified as Pichia udriavzevii/Issatchenkia orientalis. P. kudriavzevii/I. orentalis is a generally recognized as a safe organism. In addition, methionine produced by K1 and C1 yeast hydrolysate yielded 1.3 ± 0.01 and 1.1 ± 0.01 mg g(-1) dry cell. Yeast strain K1 may be suitable as a potential source of methionine for dietary supplements in organic poultry feed but may require growth conditions to further increase their methionine content.

Biotechnological approaches for the value addition of whey

Whey, the liquid remaining after milk fat and casein have been separated from whole milk, is one of the major disposal problems of the dairy industry, and demands simple and economical solutions. In view of the fast developments in biotechnological techniques, alternatives of treating whey by transforming lactose present in it to value added products have been actively explored. Whey can be used directly as a substrate for the growth of different microorganisms to obtain various products such as ethanol, single-cell protein, enzymes, lactic acid, citric acid, biogas and so on. In this review, a comprehensive and illustrative survey is made to elaborate the various biotechnological innovations/techniques applied for the effective utilization of whey for the production of different bioproducts.

Methionine production by fermentation

Fermentation processes have been developed for producing most of the essential amino acids. Methionine is one exception. Although microbial production of methionine has been attempted, no commercial bioproduction exists. Here, we discuss the prospects of producing methionine by fermentation. A detailed account is given of methionine biosynthesis and its regulation in some potential producer microorganisms. Problems associated with isolation of methionine overproducing strains are discussed. Approaches to selecting microorganism having relaxed and complex regulatory control mechanisms for methionine biosynthesis are examined. The importance of fermentation media composition and culture conditions for methionine production is assessed and methods for recovering methionine from fermentation broth are considered.

Methionine production by microorganisms

Microbial production of methionine is reviewed with 73 references. The review describes different methionine-producing organisms, as well as analog-resistant regulatory mutants, their optimum cultural conditions and yields. The pathways of methionine biosynthesis and their regulation are discussed.