In order to improve the acidity of fermented walnut milk, the effects of different sugars and protein concentrations on the fermentation characteristics of walnut milk were investigated. The sugar composition and fermentation characteristics of reconstituted milk, soybean milk and walnut milk were comparably determined. The results showed that there were few fermentable sugars in walnut milk, which resulted in the low acidity of fermented walnut milk, thus additional carbon source should be added to improve the fermentation. By adding glucose or sucrose, sucrose was more conducive to acid production than glucose for walnut milk. The optimum adding amount of sucrose was further determined to be 7.0% (mass fraction) by sensory evaluation. The trichloroacetic acid - soluble nitrogen and buffering capacity of walnut milk under different protein concentrations (1.0%-3.0%) (mass fraction) were determined, along with the pH, acidity and viable counts of fermented walnut milk. The results showed that protein concentrations were positively proportional to the acidity and buffering capacity (R2>0.995). With pH ≤4.5, acidity ≥30.0 °T as the end point of fermentation, the optimum protein concentration for fermented walnut milk was 2.0% (mass fraction) according to the fermentation characteristics, texture characteristics and sensory evaluation. The prepared fermented walnut milk had moderate sour and sweet taste, with uniform texture and light walnut aroma. The experimental results can provide a theoretical basis for the industrial application of fermented walnut milk.
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