Enzymatic firming of high-pressure frozen strawberry halves by means of exogenous pectinmethylesterase
Van Buggenhout, S.; Maes, V.; Messagie, I.; Duveiter, T.; Van Loey, A.; Hendrickx, M.
Communications in Agricultural and Applied Biological Sciences 70(2): 259-262
2005
ISSN/ISBN: 1379-1176 PMID: 16366321 Document Number: 592782
The potential of high-pressure shift freezing (HPSF) in the reduction of freezing damage in frozen strawberry fruits was evaluated. The efficacy of vacuum infusion of exogenous pectin methylesterase (PME) with calcium as a pre-freezing treatment to reduce texture loss in frozen strawberries was also evaluated. Fruits of cv. Elsanta were stored for 3 days at 2 degrees C, halved, and infused with Aspergillus aculeatus PME and calcium chloride. The fruits were frozen slowly in stagnant air at -18 degrees C. After equilibrium of the whole pressure system, the pressure was increased up to 200 MPa. The system was cooled down until the temperature at the centre of the sample reached -15 degrees C. The pressure was restored to atmospheric pressure. The samples were transferred to a conventional freezer for overnight storage at -18 degrees C. The fruits were successfully infused with PME and calcium chloride under vacuum for 5 minutes at room temperature. PME/Ca-infused fruits were harder than fresh fruits (by approximately 2-fold) and water-infused fruits. Approximately 5 h and 17 minutes were required to completely freeze fruits in stagnant air at -18 degrees C. During HPSF, the samples started to freeze at pressure release. From this point, 33 minutes were required to completely freeze the fruits. The nominal freezing time of HPSF was lower than that of conventional slow freezing. The hardness and weight of fruits subjected to slow freezing were reduced by ~87 and 40%, respectively, upon thawing, suggesting that this method did not strikingly prevent quality loss in frozen fruits. Hardness retention was enhanced by HPSF, and PME-Ca-infused fruits frozen by HPSF were harder than fresh fruits. Infusion with PME did not prevent texture loss in the samples.