Glucoamylase is one of the oldest and widely used biocatalysts in food industry. The major application of glucoamylase is the saccharification of partially processed starch/dextrin to glucose, which is an essential substrate for numerous fermentation processes and a range of food and beverage industries. Glucoamylase for commercial purposes has traditionally been produced employing filamentous fungi, although a diverse group of microorganisms is reported to produce glucoamylase, since they secrete large quantities of the enzyme extracellularly. The commercially used fungal glucoamylases have certain limitations such as moderate thermostability, acidic pH requirement, and slow catalytic activity that increase the process cost. Consequently, the search for newer glucoamylases and protein engineering to improve pH and temperature optima leading to amelioration in catalytic efficiency of existing enzymes have been the major areas of research over the years. The present review focuses attention on the recent advances in molecular biology and protein engineering of glucoamylase to improve its production and functional properties including the so far success achieved in isolating mutants with enhanced thermostability and selectivity, higher pH optimum and improved catalytic activity. A comprehensive account is included on the diversity, regulation of production, classification, purification and properties, and potential applications of microbial glucoamylases to provide an overview on all the important aspects of the enzyme.

Microbial glucoamylases: characteristics and applications

Fermentation has been used for several thousand years as an effective and low-cost resource to preserve the quality and safety of foods. Apart from this primary role, fermentation adds value and enhances nutritional quality and digestibility through biological enrichment, and provides dietary enrichment through aroma and flavour production and modifying textures of food substrates. All these changes are operated by microorganisms, which, naturally present (spontaneous fermentations) or added (inoculated fermentation) in raw materials, break down complex carbohydrates and proteins into more easily digestible elements. Among the fermentation microorganisms, yeasts are undoubtedly the most important group of microorganisms that are exploited for commercial purposes. Yeasts used in food fermentation processes modify original materials organoleptically, physically and nutritionally and for this they have been used for millennia in bread-making and production of alcoholic beverages. A diversity of fermented foods, which vary according to geographical area and cultural preference, are produced across the globe and the individual and peculiar characteristics which distinguish and typify each food are determined by the expression of the wide biodiversity of the fermenting microorganisms, such as yeasts. In Western countries yeasts are involved in the production of kefir from milk, beer from barley and hops, and wine from grapes, while in developing countries, where the lack of resources limits the use of techniques such as vitamin enrichment of food and the use of capital-intensive processes for food preservation, food fermentation contributes substantially to food security. In these countries there is a wide diffusion of traditional fermented foods, produced from both edible and inedible raw materials, based on local customs and generally consumed as dietary staples. Here we report the ecology and the role of yeasts involved in fermented food and beverages, focusing on the dominant species and their effect on the product quality, summarised in Table 2.1. Chapter 2

Taxonomic and Ecological Diversity of Food and Beverage Yeasts

Fresh acid-curd cheeses refer to those varieties produced by the coagulation of milk, cream or whey via acidification or a combination of acid and heat, and which are ready for consumption once the manufacturing operations are complete (Fig. 1). They differ from rennet-curd cheese varieties (e.g. Camembert, Cheddar, Emmental), where coagulation is induced by the action of rennet at pH values of 6.4–6.6, in that coagulation occurs close to the isoelectric point of casein, i.e. pH 4.6, or at higher values when elevated temperatures are used, e.g. in Ricotta (pH 60 to 80°C). While a very small amount of rennet may be used in the production of Quarg, Cottage cheese and Fromage frais to give firmer coagula and minimize casein losses (on subsequent whey separation), its addition is not essential.

Fresh Acid-Curd Cheese Varieties

The effect that yeast research and development on yeasts has had on the brewing industry is traced from the time of Pasteur to the present time.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2050-0416.1986.tb04453.x

One hundred years of yeast research and development in the brewing industry

Egg white gels were formed by heating liquid egg white at various pH, protein, and NaCl levels at different temperatures and times of heating. Hardness, cohesiveness, and springiness of gels were measured. Serum was expressed from gels and evaluated by polyacrylamide gel electrophoresis. Selected samples were prepared for scanning electron microscopy. Gel hardness rose with increasing temperature, time, pH, and protein level, and decreased with added salt. Cohesiveness and springiness increased with time and temperature of heating. Expressed serum decreased as pH, time, temperature, and protein level were increased. Gels at pH 5 and 6 had a coarse, aggregated structure. At pH 9 protein strands and globules were arranged in a uniform matrix. Salt prompted aggregation of gels.

Texture and Microstructure of Heat‐Formed Egg White Gels

Biochimie et physiologie des levures du genre Saccharomyces. Techniques de fusion des spheroplastes et de transformation genetique chez les levures de brasserie. Applications

Genetic manipulation of brewing and related yeast strains

The selection and modification of brewer's yeast strains☆

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Genetic manipulation of brewing and related yeast strains

The selection and modification of brewer's yeast strains☆