Enzyme, Temperature, and Processing Effects on the Percentage of Juice Recovery and Anthocyanin Changes in Blueberries

A small-scale fruit press (5.5-L Ferrari stainless/aluminum) plus and minus heated mash treatments with two pectinase enzymes was utilized to determine the percentage of juice recovery (%JR) in fresh vs. frozen rabbiteye (RAB) and southern highbush (SHB) blueberries.  To determine optimal large-scale juicing protocols, a press sack was produced using a medium-weave polyester mesh (#2636) that was also used in follow-up pilot-scale hydraulic pressing on a Goodnature X-1.  All presses were at least triplicated.  Lack of gelling and %JR served as the critical processing points of interest.  In the Ferrari, 500, 750, and 1,000 g fruit were initially tested using frozen, thawed 'Tifblue' (RAB), not heated, no enzymes, and %JR was 73.1% (± 1.9), 72.7 (± 1.6), and 74.4 (± 0.4%), respectively.  Although numerically indifferent, the 1,000 g presses were easier to press, and delivered the most uniform cakes.  Using 1,000 g berries heated to 85 °C marginally increased %JR (76.9 ± 1.1%).  Then, commercial-like mixes of 1,000 g SHB ('Columbus', 'Montgomery') and RAB ('Magnolia', 'Biloxi') were evaluated fresh, frozen, via heated mashes (95 °C for 3 min.) ± enzymes (AB Enzymes Rohapect 10L and Novozyme Pectinex BE XXL).  In fresh SHB pressed at room temperature %JR was low (42.1 ± 4.6%) due to gelling yet, increased markedly when mash was heated to 95 °C (71.1 ± 1.8%).  RAB and SHB delivered different %JR when pressed after thawing at ambient temperatures (45.9 ± 6.0% vs. 61.4 ± 7.4%).  Heating markedly improved %JR in both RAB and SHB to 60.8 ± 6.3% and 68.6 ± 2.6%, respectively.  Adding either enzyme after heating did not significantly improve %JR in RAB or SHB.  Heating mashes increased °Brix released (about 3° to 4°), and adding enzymes resulted in the highest sugar content in RAB (15.6) and SHB (17.4 °Brix) mixtures, and in 'Tifblue' (14.1).  'Tifblue' fruit (27.5 Kg) was heated in a 40-L steam-jacketed kettle up to 95 °C for 2 min and %JR was 74.0 ± 1.0%.  Raw blueberries, press cakes, and clarified and non-clarified juice samples were analyzed for anthocyanidins.  Cyanidin, delphinidin, malvidin, peonidin, and petunidin were recovered in all processing steps, with the press cake having the highest anthocyanidins, especially cyanidin, while the clarified NFC (not-from-concentrate) pasteurized juice contained the least.  The common 15 sugar-anthocyanin conjugates in blueberries were recovered along with several already reported acetyl glucosides, and additional acetyl and courmaroyl glucosides that have not been reported in the literature.