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Food Microbiology 28 (2011) 1426e1431

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Food Microbiology
journal homepage: www.elsevier.com/locate/fm

A comparative study of changes in the microbiota of apple juice treated by high hydrostatic pressure (HHP) or high pressure homogenisation (HPH)
Alan M. McKay*, Mark Linton, Jennifer Stirling, Aideen Mackle, Margaret F. Patterson
FoodMicrobiology Branch, Agriculture, Food and Environmental Science Division, Agri-Food and Biosciences Institute, Newforge Lane, Belfast BT9 5PX, Northern Ireland, UK

a r t i c l e i n f o
Article history: Received 22 February 2011 Received in revised form 7 June 2011 Accepted 22 June 2011 Available online 13 July 2011 Keywords: Apple juice High hydrostatic pressure High pressure homogenisation FrateuriaFruit

a b s t r a c t
The objective of this study was to assess the effect of High Pressure Homogenisation (HPH) compared with High Hydrostatic Pressure (HHP) on the microbiological quality of raw apple juice during storage at ideal (4  C) and abuse (12  C) temperatures. In the case of HPH, only low numbers of micro-organisms were detected after treatment at 300 MPa (typically between 2 and3 log.mlÀ1). These were identified as Streptomyces spp., and numbers did not increase during storage of the juice for 35 days, irrespective of storage temperature. In the case of HHP, the total aerobic counts were also reduced significantly (p < 0.05) after treatment for 1 min at 500 and 600 MPa and the numbers did not increase significantly during storage at 4  C. However, during storage at 12  Cthe counts did increase significantly (p < 0.05) and by day 14 counts at 500 MPa were not significantly different from the control juice. This confirms that good temperature control is important if the full benefits of HHP treatment are to be realised. Frateuria aurantia dominated the microbiota of the HHP apple juice stored at 12  C along with low levels of Bacillus and Streptomyces spp. The HPHand HHP juices both turned brown during storage indicating that neither treatment was sufficient to inactivate polyphenol oxidase. The enzyme is known to be pressure resistant and this discolouration was controlled by a heat treatment (70  C for 1 min) used in commercial practice and given prior to HP treatment. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction The food industry continuesto be interested in the use of minimal processing technologies as a way of meeting consumer demand to extend shelf-life, without the need for chemical preservatives and without compromising the wholesomeness and safety of foods. The retention of fresh-like characteristics and nutritional quality are particularly important in certain foods, such as fruit juices, and can be used in the marketingstrategy for premium added-value products. One of the most promising of the nonthermal processing methods is high hydrostatic pressure (HHP). This technology is already used commercially around the world for a variety of foods, including cooked meats, shellfish, fruit and vegetables juices, sauces and dips (Norton and Sun, 2008; Sampedro and Fan, 2010; Gassiot and Masoliver, 2010) and in 2001 theEuropean Commission authorised the sale of fruit juice pasteurised by high pressure (Anonymous, 2001). Fruit juices are normally treated at 400 MPa or greater for a few minutes at 20  C or below. This is sufficient to

* Corresponding author. E-mail address: alan.mckay@afbini.gov.uk (A.M. McKay). 0740-0020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.fm.2011.06.013significantly reduce the numbers of spoilage micro-organisms, such as yeasts, moulds and lactic acid bacteria and extend refrigerated shelf-life to w30 days (Patterson, 2005). An alternative promising technology is High Pressure Homogenisation (HPH). HPH involves the pumping of a liquid at high pressure (over 100 MPa) through homogenising valves. Unlike HHP, HPH is not yet used commercially....
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