Bench scale batch steam explosion of Florida red and white grapefruit juice processing residues

Abstract

Florida juice processors amassed 51,000 metric tons of grapefruit juice processing residues (GFPR) in the 2018-19 season. GFPR contain valuable compounds such as pectic hydrocolloids, peel oil, sugars, phenolics and flavonoids that are ultimately lost or destroyed when they are converted to low value animal feed and molasses. If these compounds could be isolated from GFPR rather than destroyed, they could be converted to high value products. In this work, red and white GFPR were subjected to steam explosion in a batch system at 130, 150 and 170°C and 1, 2, 4 and 8 min holding time to identify the conditions for maximum recovery of pectic hydrocolloids, peel oil, sugars, phenolics and flavonoids. Steam explosion at 170°C and an 8 min hold time resulted in the recovery of 56-85% of total available glucose and fructose and the volatilization of 68-98% of the available peel oil. Of the phenolics and flavonoids analyzed, 61-62% could be extracted using steam explosion. Maximum recovery of pectic hydrocolloids, estimated by galacturonic acid content, was 1.6446 g • 100 g−1 for red GFPR at 130°C – 8 min and 1.557 g • 100 g−1 for white GFPR at 150°C – 2 min.