High pressure processing for the extension of Laminaria ochroleuca (kombu) shelf-life: A comparative study with seaweed salting and freezing

The effect of high pressure processing (HPP) at 400 and 600 MPa for 5 min on Laminaria ochroleuca (kombu seaweed) shelf-life during storage at 4 degrees C for 180 days was investigated. Viable bacterial counts increased in untreated kombu from 5.42 log cfu/g on day 1 to 8.47 log cfu/g on day 60 while they declined in HPP-treated kombu to 2.53-3.62 log cfu/g on day 1 and remained below 3 log cfu/g during storage. Salting with 40% marine salt and freezing at - 24 degrees C also achieved significant decreases of viable bacterial counts, to levels of 3.94 and 2.75 log cfu/g, respectively, on day 60. Kombu pH, dry matter, water activity, colour parameters and texture parameters were significantly influenced by the preservation procedure. Total polyphenol content and antioxidant capacity of kombu samples did not differ on day 1, but on day 180 frozen kombu retained 71.9% of the initial polyphenol content versus 18.7-19.3% in HPP samples and 14.2% in salted samples, and 78.7% of the initial antioxidant capacity versus 22.2-23.1% in HPP samples and 18.3% in salted samples. Proteolytic activity and aminopeptidase activity were more affected by HPP than by salting or freezing on day 1, although all the samples showed similar values afterwards. Industrial relevance: HPP, salting and freezing showed to be valid preservation procedures from the point of view of kombu microbiological quality, achieving a shelf-life of at least 180 days. Total polyphenol content and antioxidant capacity remained at higher levels in frozen kombu than in HPP and salted kombu after storage for 180 days.