Moisture absorption and dynamic flavor changes in hydrolysed and freeze-dried pine nut (Pinus koraiensis) by-products during storage

In the present study, two different fractions of pine nut (Pinus koraiensis) protein hydrolysate powder (PNPHP1-3 (kDa) and PNPHP3-10 (kDa)) were prepared and stored for fifteen days at 25 degrees C and 50% relative humidity. Changes in moisture absorption, secondary structure and flavor compounds were measured at various time intervals over fifteen days. Results showed that the PNPHP3-10 (kDa) had higher moisture absorption capacity from day 6 to day 15 and that the secondary structure of two PNPHP fractions was changed. Major nine and eight flavor compounds were identified from PNPHP1-3 (kDa) and PNPHP3-10 (kDa), respectively. PNPHP1-3 (kDa) mainly generated aldehydes and PNPHP3-10 (kDa) generated pyrazines. Finally, the formation of pyrazines was conjectured. The data suggests that Maillard reaction, microbial fermentation and lipid oxidation occurred during storage. The reactions appeared to be strongest by the sixth day.