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Publication Title | Concentration of Apple Juice Using Spinning Disc Reactor Technology

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Food

Processing & Technology

Akhtar et al. J Food Process Technol 2011, 2:2 http://dx.doi.org/10.4172/2157-7110.1000108

Research Article Open Access

Concentration of Apple Juice Using Spinning Disc Reactor Technology

Mahmood Akhtar*, Philip Chan, Novi Safriani, Brent Murray and Graham Clayton

School of Food Science and Nutrition, University of Leeds, Leeds LS2 9JT, UK

Abstract

The use of spinning disc reactor (SDR) technology for the concentration of apple juice was investigated. The apple juice was passed over the SDR disc spinning at 2000rpm, heated at 90-120°C, and at a ow rate of 7mL s-1. Experimental results showed that the SDR has no signi cant detrimental effects on the physicochemical properties and quality of the apple juice after the concentration process, despite using high processing temperatures (90- 120°C). Due to the short residence time of the SDR, the thermally-induced colour change of the concentrates has been minimized. All apple juice concentrate samples exhibited narrow particle size distributions with the average particle size in the range 0.1 to 12μm. The SDR-made reconstituted apple juices are comparable to both the original pure-pressed apple juice sample and the commercial reconstituted product. Volatile components (ester, aldehyde and alcohol) collected during the concentration process were analyzed with GC-MS, and the analysis suggests the formation of new aroma compounds (ethyl acetate, n-butyl alcohol and 2-hexenal) which can be added back to the reconstituted apple juice to enhance its sensory quality.

Keywords: Concentration; Spinning disc reactor; Apple juice concentrate; Physicochemical properties; GC-MS

Introduction

Fruit juices are o en concentrated to reduce their weight and volume, and thus to reduce their packaging, transportation and storage costs. Concentrated juices are biochemically stable and have a long shelf life due to the reduction in the water activity [1]. However, conventional thermal concentration techniques are known to cause losses of avour and aroma compounds, and have consequent undesirable e ects on the avour characteristics of the juice products [2].

e aroma components of apple juice usually comprise a mixture of volatile organic compounds, principally esters, aldehydes and alcohols, but also ethers, fatty acids, lactones, terpenes and ketones [3]. In general, the concentration of individual aroma components in the apple juice ranges from less than 1 to 20ppm [4,5]. Each of these compounds gives a typical character to the apple juice avour. During conventional thermal concentration processing, many of these volatile compounds present in the apple juice are transformed (due to high temperature) or lost (via water vaporization). e detrimental e ects were also reported in the manufacturing process of other fruit juice such as orange juice [6,7] and pineapple juice [8]. ese undesirable e ects can be signi cant, Peredi [9] reported more than half of the tested volatile compounds were lost compared to the unprocessed apple juice and Su and Wiley [10] demonstrated that almost all volatile compounds in apple juice are lost during the thermal processing. To generate a avourful product, these aroma compounds must be recovered and added back to the concentrate [11]. erefore, it is important to select the suitable technology for food processing, especially for heat sensitive compounds, to produce high nutritive value and appreciable organoleptic quality of the products.

In light of maximizing the e ciency of the concentration process while maintaining the nutritional and sensory qualities of the nal product, the spinning disc reactor (SDR) could be an alternative technology in the production of fruit juice concentrates. e SDR has been widely used in emulsi cation, chemical and pharmaceutical industries [12-15]. Recently, we have used the SDR technology in pasteurizing carrot juice [12]. e results showed that the pasteurization process is more controllable than the conventional technologies. Not only was the processing time much reduced, but the quality of the juice

J Food Process Technol

ISSN:2157-7110 JFPT, an open access journal

was also retained. No signi cant colour change was observed in the SDR-processed juice compared to the fresh juice sample.

e SDR (type P201) used in this study (Figure 1) is comprised of a 20 cm diameter disc with a heating and cooling facility in the range of + 250°C to – 20°C by using heat transfer uid (Paratherm OR) in a recirculation bath. e spinning disc has a speed range of 100 to 3000rpm with sample feed rates in the range 0.5 to 7mL s-1. e main vessel has been mechanically designed to withstand pressures up to 5bar. A selection of two standard pumps can be incorporated to the main controller, depending on the viscosity of the feed material or the liquid sample to be used. e SDR technology works on the principle that the feed liquid passes across the surface of a metal disc which can be programmed to spin at controlled speeds, subjected to heating and cooling at according to the product requirements. e centrifugal force causes the liquid to form a very thin (typically several μm in thickness) lm on the disc, which gives very high heat transfer coe cients between the disc and the liquid, as well as very high mass transfer between the liquid and the gas phase above the liquid lm. e residence time on the disc is short, typically less than a second, so that rapid pasteurization, followed by rapid cooling on the walls beyond the disc edge, can be achieved. An inert carrier gas can also be introduced to the system during the concentration process to facilitate evaporation (Figure 1). In addition, the SDR method can be applied as a continuous process on industrial scale.

In order to explore the potential of this new technology for the food and drink industry, the aim of this work was to employ SDR for the production of apple juice concentrate and to evaluate the e ciency of

*Corresponding author: Mahmood Akhtar, School of Food Science and Nutrition, University of Leeds, Leeds LS2 9JT, UK, Tel:+44 (0) 113 3432952; fax: +44 (0) 1133432982; E-mail: m.akhtar@leeds.ac.uk

Received January 20, 2011; Accepted March 25, 2011; Published March 27, 2011

Citation: Akhtar M, Chan P, Safriani N, Murray B, Clayton G (2011) Concentration of Apple Juice Using Spinning Disc Reactor Technology. J Food Process Technol 2:108. doi:10.4172/2157-7110.1000108

Copyright: © 2011 Akhtar M, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Volume 2 • Issue 2 • 1000108

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