in recent years, Chinese scholars began to study the production technology of enzyme food. Angel and others used yeast and lactic acid bacteria to ferment Zizyphus jujuba, and determined the best technological parameters as follows: at 3℃, .1% yeast was inoculated and fermented for 12h； hours; Inoculate .5% lactic acid bacteria starter at 37℃, let it stand for 28 hours, then control the temperature to 6~8℃, let it stand for 24 hours, make it ferment, and then make the fermented liquid fragrant [6]. Taking protease activity as an index, Nanzhu et al. used Box-Behnken Design 8..5v response surface method to optimize the optimum technological parameters for producing pineapple peel residue enzyme, which were fermentation temperature 23℃, yeast inoculation amount .3% and fermentation time 16.5h [7]. With the contents of reducing sugar, flavonoids, protein, total acid and soluble solids as indicators, Zhang Weihong and others optimized the conditions of Chuju fruit enzyme products by orthogonal test: the addition of pitaya 15g/L, Chuju 6g/L, white sugar 145 g/L and fermentation for 3 days [8]. Fu Qingquan and others adopted single factor experiment and orthogonal experiment, and determined that the optimum processing parameters of fermented taro flour bread were as follows: the addition of yeast powder 3%, taro powder 6%, yeast 2% and sugar 16% [9].
2.2 Agricultural Enzymes
Fang Sheng and other scholars found that the agricultural enzymes made from yellow rice syrup instead of clear water as ingredient water, leafy vegetables including radish leaves, Chinese cabbage leaves and lettuce leaves as plant raw materials, and mixed with red sugar were more nutritious [1]. The preparation process of liquid enzyme bacterial fertilizer described by Liu Cuiwen is as follows: bean cake, microbial inoculum and grass or vegetable leaves washed in advance and cut into 1-2 cm long are put into a tank in turn, accounting for about 8% of the solvent; Inject clean water, cover the raw materials with breathable cloth or paper; Stir with a clean wooden stick every morning and afternoon for 5 minutes; It can be used in 3~4d in summer and 7~1d in winter when bubbles emerge and yellow-green liquid appears [11].
3. Possible safety risks in the preparation process
The biological hazards that are easy to occur in the preparation process of enzyme include: the contamination of poisonous bacteria due to incomplete disinfection of utensils and lax sealing in the fermentation process; The metabolic process of compound fermentation bacteria is easily influenced by the external environment, and the metabolites are uncontrollable; The composition of raw materials is complex, and toxic by-products are produced in the fermentation process; After long-term use, the strains may mutate into toxic strains, which will affect the quality of products [12]. Secondly, chemical hazards are mainly included in the treatment of raw materials of some fermented products, and some chemicals are not easy to be completely removed, including chemical reagents, heavy metal ions and pesticide residues. There are some potential physical poisons in the preparation process, mainly including sand, hair and iron rust residues [13].