Effect of high pressure processing on the quality of acidified Granny Smith apple purée product

The aim of the present study was the evaluation of the physicochemical, nutritional and microbial quality of acidified Granny Smith (GS) apple purée processed on industrial-scale high pressure system during 3 weeks of refrigerated storage (5 °C ± 1 °C). Two commercially feasible pressure treatments (400 and 600 MPa/5 min/20 °C) and a mild conventional pasteurization at 75 °C/10 min, with pasteurization values of P70°C7.5 = 8.15 min, were conducted and their effect on total vitamin C (total Vit C), ascorbic acid (AA) and total phenolic content (TPP), and on instrumental quality parameters (color, viscosity, soluble solids, titratable acidity and pH) were comparatively studied. Inactivation of indigenous microorganisms (total aerobic mesophilic and psychrotrophic counts and moulds and yeasts) of the apple product was also studied and monitored during storage. Total Vit C and AA contents were unaffected by the 400 MPa and the mild pasteurization treatment. TPP content was not changed during processing at 400 MPa, but was affected by the 600 MPa and also slightly by the pasteurization treatment. Experimental data on the loss of total Vit C during storage were described with a first-order reaction kinetic and times of half loss between 9.3 to 10.3 days could be estimated for the three studied processes. Storage provoked loss of TPP content and color deterioration of pressurized GS puree samples, which was attributed to enzymatic browning reactions. Microbial counts were reduced by the different preservation techniques below the detection limit (50 cfu g−1) and storage revealed no further growth.Industrial relevanceThis is one of the first studies applying commercial industrial-scale high pressure equipment for the pasteurization of an acidified apple purée product. The pressures of 400 and 600 MPa with 5 min holding time at ambient temperature render economically feasible processes with high throughput and productivity. In the European Union the most important fruits in terms of production are apples. Apple purée is a largely consumed preserve in many households and beside apple juice or cider is one of the most important apple products in the market. In contrast to traditional apple purée preparation, high pressure processing or mild thermal treatments could imply new opportunities for the apple processing industry in developing more fresh-like, value-added apple products with reasonable shelf life.

Research Highlights
► Mild High pressure processing (400 MPa) provide a non-thermal technology to pasteurize Granny Smith purée with a shelf life of 21 days.
► 400 MPa pressurisation and the mild conventional pasteurisation did not affect adversely the initial instrumental and nutritional quality of the Granny Smith purée.
► However during storage at 5ºC none of the treatments prevented fully undesirable changes during shelf life.
► Quality constraints could be overcome by using another apple cultivar with lower browning tendency or by incorporating other more powerful antibrowning agents.