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Integrated research on agricultural waste reclamation

Introduction
Production of yeast from soybean cooking waste at miso factories
Application of soy waste as koji substrate for rice miso manufacturing (5, 6)
Conclusion
References
Discussion summary

Hideo Ebine

Applied Microbiology Division, National Food Research Institute, Ministry of Agriculture, Forestry and Fisheries, Tokyo, Japan

Introduction

A stable supply of feedstuffs is an absolute necessity for the sound development of the animal and fishery industries in Japan. However, the recent trend, particularly in 1972 - 73, towards world-wide constraints on foodstuff supplies has caused sharp rises in animal feed market prices. In order to cope with this, research efforts have been accelerated to improve forage production. However, our domestic feed supply is limited because most of the arable land is already cultivated, and because climatic conditions control how much can be grown. The forage supply in Japan is sufficient to meet the requirements of dairy cows and beef cattle, but hogs and poultry require a much higher concentration of protein in their feed than cattle do.

Constant supplies of soybean meal and fish meal, major sources of feed protein, will not always be ensured in view of the drastically changing patterns of crop marketing and reduced availability of fish in the world. These circumstances justify the development of alternative feed proteins, among which single-cell protein (SCP) is of prime importance. Although there are many possible substrates on which to grow SCP, production technology based on the exploitation of agricultural, forestry, and fishery waste materials is of the greatest significance, both from the standpoint of resources and environmental preservation.

In 1975, a national project to develop novel microbial protein foodstuffs from agro-waste was begun by several research institutes in the Ministry of Agriculture, Forestry, and Fisheries. These efforts are to last until 1980.

Table 1 lists the investigations being undertaken on SCP production by the National Food Research Institute, the National Forest Research Institute, and the Tokai Regional Fisheries Research Laboratory, with the assistance of the associated prefectural institutes. In addition, investigations on methods to assess the safety, feed value, and acceptability of SCP products, as well as the means to pelletize and store them, are being developed by the National Institute of Animal Health and the National Institute of Animal Industry. The most promising current potential wastes for SCP production in Japan are also listed in Table 1. These materials are available in bulk at nominal price, or even at a negative price from the food industries and forest industries.

TABLE 1. Potential Agricultural and Fishery Wastes and Institutes Where Their Utilization Is Being Studied in the Ministry of Agriculture, Forestry and Fisheries

* National Food Research Institute
** Kushiro Fishery Research Laboratory

Cooking waste results from the processing of miso, typical fermented soybean food in Japan. The treatment to reduce the chemical oxygen demand (COD) before discharging the waste into a river is very difficult because the COD level is so high, and because it is extremely foamy. Consequently, much research has been conducted in this area (1). The subject will be treated in more detail in a later portion of this paper.

Citrus waste is discharged mainly from the juice and canning processing of Citrus unshiu, a popular fruit in Japan. The waste, estimated to amount to approximately 350,000 tons per year, is pressed again after liming to obtain the secondary juice; this juice accounts for 50 per cent of the initial waste (2). The secondary juice, containing about ten per cent sugar, can be used as an SCP substrate. This secondary waste, which is currently dehydrated in rotating dryers for making compound feed, can also serve as a solid medium for fungus cultivation in order to raise its protein level.

A large amount of cellulosic residue is also available in Japan. The key to its use for SCP production is in developing methods to treat the materials in order to produce fermentable carbohydrate economically. Possible treatments of agro-waste materials through mechanical, chemical, and biological degradation are being intensively investigated. For example, using a cryomill, one can obtain, in a short time, a fine rice husk powder of 250 mesh or even smaller particles. The cellulosic powder, which lacks the normal fine-structure crystallinity of cellulose, is easily degrated by enzyme treatment, particularly after delignification with 1 per cent NaOH solution. Cryomill processing is promising because energy for cooling is available as a by-product from the evaporation of liquid natural gas in Japan.

The large amount of waste from the fisheries industry is an urgent problem because of water pollution. Each year, 2,700,000 tons of fish processing waste containing 6 per cent dry matter are discharged from fish meal factories. The dry matter amounts to 160,000 tons, of which 50,000 tons are utilized as feed after condensing and dehydration. The other 110,000 tons have yet to be utilized. An investigation is being undertaken to utilize this waste, which contains protein and oil, as an SCP substrate, employing a fish oil-assimilating fungus, Aspergiflus tamarii, isolated from tamari-miso, which in itself contains a comparatively high level of oil.

Special considerations are paid to the safety of both the ingredients and the microorganisms selected for processing. In screening tests, suitable micro-organisms have been isolated from the traditional fermented foods such as miso, shoyu, and sake in Japan. For example, as shown in Table 2. Aspergillus oryzae, A. sojae, and A. tamarii are widely employed in the fermented food industries. The total amount of koji, the fermented products of these fungi, is approximately 900,000 tons per year. The mycelium content of koli, as determined by Arima (3), differs widely depending upon the ingredients and culture conditions, including duration, temperature, relative humidity, level of oxygen and carbon dioxide in the fermenting facility, and mechanical agitation of the materials. The total amount of mycelium in koji is calculated to be approximately 73,000 tons, which have been traditionally eaten as part of miso, shoyu, sake, and other fermented foods made with koji. This fact is very important for the acceptance of novel microbial protein either as a food or feed prepared with Aspergillus oryzae or its related strains.

TABLE 2. Amount of Mycelium in Aspergillus for Several Kinds of Koji Food Processing in Japan

Production of yeast from soybean cooking waste at miso factories

Because soybean cooking waste has such a high COD value, it is one of the most difficult of all food industry wastes to treat in Japan. Consequently, there are many devices to treat soybean cooking waste via mechanical, chemical, or biological methods.

In 1970, an industrial co-operative was formed to treat this waste. It was established by nine members from a miso factory at Maruko, Nagano Prefecture (4). This is the sole factory in Japan where SCP is being made from agro-industrial waste, except for factories that make torula yeast from spent sulphite liquor.

As shown in Figure 1, soybean cooking waste is sent to the factory by tank trucks or pipelines directly from the miso factory cookers. After the pH value is adjusted to 4.0 in a serving tank, the waste is transferred into a Waldhof continuous fermenter of 15 kl capacity. In the fermenter, Torulopsis xylinus is cultivated, with an anti-foaming agent, at 30°Cat a dilution rate of 0.3 - 0.4 hr(-1) without any other nutrient supplements. Maximum production of dehydrated yeast is 800 kg when 80 tons of waste are supplied and COD is reduced by 70 - 75 per cent. For purpose of lowering production costs, the yeast milk, after washing and heating at 80°C for 30 min., is often delivered to neighborhood farms.

Figure. 1. Flow Diagram of Production of Fodder Yeast from Soybean Cooking Waste

At present, this method has problems that must be solved: (i) the 70 - 75 per cent COD reduction rate should be raised still further; (ii) microbial contamination, originating mainly during transportation of the waste in tank trucks, must be eliminated; and (iii) the process, although small in scale, requires trained technologists to conduct it properly, resulting in higher costs to the consumer.

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