生物论文代写 Nestl Expanded Beyond Its Traditional Product
生物论文代写 Nestl Expanded Beyond Its Traditional Product
Work Nature and Scope
The work nature of this project is mainly laboratory analysis and pilot simulation.
At the beginning of the attachment, training on general microbiological techniques and the operation of laboratory equipment were conducted. After preparation for background knowledge, laboratory scale hydrolysis runs were started on the inhibition of general pathogen growth, following with microbiological analysis of the fermentation. Many other tasks were undertaken during the internship period. Nevertheless, minor tasks that are of low relevance to main scope of will not be discussed in details in this report.
Attachment Duration
The attachment lasted 22 weeks from 11th Jan 2010 to 12th Jun 2010.
REVIEW OF THEORY AND PREVIOUS WORK
Literature review on Fermentation
Fermentation, one of the oldest methods for food processing, is cardinally important to the food industry as it can be considered as a desirable microbial activity in foods. Traditionally, fermentation was used as a conservation technique for raw food material. After the fermentation, the product usually has a much longer shelf-life than the unfermented one. Fermented food products such as bread, beer, wine, soy sauce, yoghurt, and cheese have been known for a long time.
Preservation of fermented foods depends on the principles of oxidation of carbohydrates and the related derivatives to generate end-products – generally acids, alcohol and carbon dioxide. As a result of partially oxidation, the food retains sufficient energy potential to be nutritional benefit to the consumer.
During the fermentation process by food grade (lactic acid) bacteria or yeasts, food safety can be improved by the production of (lactic) acid or ethanol by these micro-organisms. The conditions generated by the fermentation are important in ensuring the microbiological safety of the products. The available carbohydrates decrease after fermentation process; they are transformed into a range of small organic molecules which exhibit antimicrobial activity, the most common being lactic, acetic, and propionic acids. In addition to the production of these inhibitory primary metabolites, many other antimicrobial components can be formed by different protective micro-organisms.
Moreover, the end-products of carbohydrate catabolism by those bacteria involved in fermentation process contribute to the flavor, aroma and texture of the products. Fermentation may also improve the nutritional quality of the food by increasing digestibility.
Koji making
General introduction to Koji
Koji was the major component of the hydrolysis substrate in the hydrolysis challenge test conducted during the attachment.
The word “Koji” means mouldy grains, which is derived from the Chinese character. The preparation of Koji is regarded as an essential step in fermentation of variety of fermented foods. Generally speaking, the process is the solid substrate cultivation of moulds to produce hydrolytic enzymes on seeds, for example, wheat or other cereals. Classes of enzymes inside Koji can catalyze the degradation of solid raw materials to soluble products, providing fermentable substrates for yeast and bacteria in the following fermentation stage. Besides the enzymes, several chemicals necessary for the fermentation process are also produced during Koji making. [2]
The advantages of Koji have generated numerous researches leading to prospective application and technological improvement. It can be used to produce several of non-food products such as antibiotics, as well as a step to provide enzymes and chemicals for subsequent food processing.
Raw material
Both whole wheat and wheat flour can be commonly used for the production of Koji, they are chosen as the raw materials due to the advantages listed below:
The less moisture content inside wheat inhibits the growth of undesirable micro-organisms, while adequate for mould growth;
Wheat assists in motivating the growth of Koji moulds;
Wheat serves as the precursors of sugars, alcohols and organic acid;
Wheat is a rich source of glutamic acid.
Usually whole wheat is first roasted and then coarsely crushed, or wheat flour which is generally steamed before use, it is to satisfy the following two contradictory factors:
To make the alpha-starch content or the enzymatic digestibility starch to a maximum level;
To make the enzymatic digestibility of protein to a maximum level.
2.2.3 Koji making procedures
Wheat
The procedures of Koji making is described in figure 1 below:
Koji mould seed culture 0.1-0.2% weight of that of raw materials
Roasting
Crushing
Moisture content 40-45%
Mixing
Culturing mould (Koji making) for 48-72 hours
Moisture content of Koji 25-35%, pH=6.5-7.0
Figure – Koji making flowchart
As illustrated in the figure, once inoculated the material with a small amount of seed mould or the pure culture of Aspergillus oryzae or A. sojae, the mixture is then spread to a large perforated stainless steel plate. The raw materials treated with heat are aerated for 2-3 days with temperature and moisture controlled air, which comes up from the bottom holes through the layer of fermenting material to give the proper conditions for mould cultivation and enzyme formation. The temperature of materials is kept at around 30oC, and moisture content of the materials decreases from 40-45% in the beginning of cultivation to 25-35% after 2 or 3 days.
This process allows the mould to grow throughout the mass and provide the enzymes necessary to hydrolyze the protein, starch and other constituents of the materials. Then, Koji, the mould cultured material making is finished. [2]
Koji enzymes
Variety of enzymes is involved in Koji, including amylase, cellulose, invertase, lipase and protease. Among those enzymes, amylase plays an important role in degradation of starch and oligosaccharides to provide substantial fermentable sugars for the following process; the proteolytic enzyme has significance on solubilisation of protein into peptides and amino acid, resulting in an increase of the soluble nitrogen yield.
General microbiological techniques practice
Before the start of the challenge test on antibiosis of the protective organism inoculated hydrolysate, it was important to be well prepared for the experiment both in theory and practical areas. As a consequence, general micro analysis techniques were learned from microbiologists in the microbiological laboratory, serving as a prelude to the coming Plant protein Koji hydrolysis challenge test. The main techniques learned were listed below; since the operation procedures were confidential, details will not be mentioned in this report.
Revival of bacteria( protective organism and Bacillus cereus) in the frozen culture;
Preparation of starter medium, performance testing of culture media;
Enumeration of cultural micro-organisms: plate count methods;
Enteriobacteriaceae Enumeration- application of Petri-film;
Detection and enumeration of presumptive Bacillus cereus with MYP agar plates;
Utilization of selective agar plates and broth to identify sort of bacteria.
Those micro techniques were well practiced by doing the routine fermentation sample analyzing work in the microbiological laboratory.