Modulation of coffee flavor precursors by Aspergillus oryzae serine carboxypeptidases

• Published in: Food science & technology 2019-10, Vol.113, p.108312, Article 108312
• Main Authors: Murthy, Pushpa S., P, Sneha H., K, Basavaraj, Kusumoto, Ken-Ichi
• Format: Article
• Language: English
• Subjects: Acid carboxypeptidase; Aspergillus oryzae; Coffee; Growth studies; Purification; Solid-state fermentation
• ISSN: 0023-6438; 1096-1127
• DOI: 10.1016/j.lwt.2019.108312

Aspergillus oryzae was isolated from coffee pulp, screened for the production of carboxypeptidase and confirmed by molecular studies. Coffee pulp posses high protease activity (1.4 × 103 nkat/mL) among the agro-substrates used for the production of proteases but wheat bran was used for further studies considering its easy availability in large volumes. Proximal composition, pre-treatment, auxiliary carbon and nitrogen with growth studies indicated carboxypeptidase activity (2.6 × 103 nkat/g). The RSM was employed to generate a predictive model of the combined effects of independent variables and indicated a significant impact on acid carboxypeptidase with 35% moisture, 30 °C temperature, 108 CFU mL−1 inoculum and 100 h duration with 4.8 × 103 nkat/g activity. The partially purified peptidase had a specific activity of 6.1 × 104 nkat/mg with a molecular weight of 50 kDa, optimal pH 3.6, temperature 35 °C and feature of a serine protease. Enzyme stability was maintained with 50% glycerol and 2 mg/mL BSA. The protease application to develop flavor profiles of coffee was noteworthy with an organoleptic score of 7.5 compared to 4.5 of the untreated sample. GC-MS highlighted enhanced flavor annotations of pyrazines contributing sweet fruit notes. Carboxypeptidase augmented the coffee bean with specialized flavor notes and has been reported for the first time. •Carboxy peptidases enzymes were extracted from the A. oryzae islolated from coffee pulp.•The SSF for peptidases was 30% moisture, 108 cfu/ml inoculum, 100 h and 30 °C.•Partial purification indicated 61287 nkat/mg with a MW 50 kDa, pH 3.6 and 35 °C.•Improved flavour annotations of pyrazines in coffee.•Serine protease was effective in improving the flavour profiles of low-grade coffee.