Abstract:

Proximate nutritional components and amino acid composition were analyzed in hydraulic macadamia nut meal.
Further, crude peptides were prepared by enzymatic hydrolysis of macadamia nut meal with either alkaline or neutral
protease. The effects of five processing conditions on the degree of hydrolysis were explored by single factor and orthogonal
array design methods in order to optimize these conditions. Results showed that hydraulic macadamia nut meal contained
32.25% protein consisting of 17 amino acids with a total content of 25.05%. The effect of five processing conditions on
the degree of hydrolysis of macadamia nut meal protein with alkaline protease was in the descending order of hydrolysis
time, reaction temperature, enzyme dosage, pH, and substrate concentration. The optimal hydrolysis conditions were found
to be reaction at 60 ℃ and pH 8.0 for 3.5 h with a substrate concentration of 110 g/L and an enzyme dosage of 2 400 U/g,
giving a degree of hydrolysis as high as 22.83%. In the case of hydrolysis with neutral protease, the decreasing order of
five processing conditions was enzyme dosage, hydrolysis time, substrate concentration, temperature, and pH, and their
optimal levels that provided maximum degree of hydrolysis as high as 22.78% were determined as 3 200 U/g, 3.5 h, 100 g/L,
55 ℃, and 7.0, respectively. In both cases, the effect of five processing conditions on the degree of hydrolysis reached up to
a significant level (P < 0.01). Under the optimized hydrolysis conditions, alkaline protease was superior to neutral protease
in preparing crude peptides from macadamia nut meal protein.

Key words: macadamia nut meal, protease, degree of hydrolysis, crude peptide