Aseptic processing of foods

An interesting vision of future uses of transport models for lhe design and scale-up of food and bioprocessing operations is also provided. Although food process design is presently dominated by the empirical approach, lhe author proposes the use of rigorous modeling and more fundamental studies and suggesls that further work is needed to predict transport properties based on basic physicochemical properties of foods. The overall idea behind the preparation of this book is justified. Foods and biological materials have certain unique characteristics compared with other process materials - one of thc prime reasons for treating food and bioengineering as a separate discipline. Transporl processes in biological materials are highly complex and hence need an independent and thorough analysis. Any book that deals with these issues should stress these unique qualities of [nod systems and show how traditional transport equations are applicable/inapplicable in different cases.

Even though the primary goal of the author was to bring out these aspec.ts, mot' needs to be clone. However, his eiforts towards making the book more understan, H}le to readers from oil.or disciplines and industry shoukl .he commended; while the mathematics, as presented in the book, is simple ,rod easy to comprehend, hut comprumises the rigor needed to solve real problems. A growing consensus amtm:4 researchers suggests that the main difierence between biological and other materials is the level of interaction between the various phases involved in transport. In biological systems phases interact ~through anti-bonding; ~r l~,nding forces) much more than in nonbiological syslems. This is the primary issue that makes biologica] systems unique. More coverage of stress interaction would have been desirable. Another issue warranting more discussion is the effect of transport phenomena on the final quality of the food product. The study of transpor! phenomena in ilself is not sufficient.

Aseptic processing, (ieveluped

in the early 1940s, is a technique by which a commercially sterilized product is filled into a pr~sterilized container, and hermetically sealed in a sterile environment, The technology for continuous processing of liquid, low-viscosity and homogeneous foods is relatively easy, and has ~czched a high degree of e'~cel]ence. However, sterilization of heterogeneous foods containing discrete particles, such as soups, sauces and ready-to-eat dishes, has been challenging and difficult. Furthermore, processing of low-acid (pH >4.6) particulate foods has been a challenging task, mainly with respect to assuring the microbiological safety and quality of aseptically-processed and -packaged products. Aseptic Processing of Foods contains 28 chapters covering eight topics, and is organized to guide readers through various facets o[ aseptic processing systems, such as presterilization of products including equipment, sterile handling of liquids and particulates, ~,ume examples of aseptically packed products, and refevant details of packaging systems. Sections on several newer advances in processing and packaging systems along with hazard analysis and testing of packaging machines for package sterilization are well written.

The effects of various process conditions/ properties on the final ";uality of the iood products, like texture, color and ilavor, needed further emphasis. As staled by the author, more rigorous modeling is needed to predict product quality changes. Although the distance to be traveled is great, this hook does provide one step toward food and biological en#neering's move to being a cliscipline in its own right. I found the hook to be an extreme!,/useful and valuable summary of the current thou'4hts on transport phenomena related to food and biological materials. Martin Okes ~tlc)~h~.,nl!(,~1,znrl f~;~)rl Pincer. f.n~lnec,m~,. 1t 46,t~ric uJtural Enl~lnl'('rin~ Bu~kJm~. ?[ttdur, Lea er~ttv. Vest L,it,iwtt[,. IN' 47~t07. [ _q.

Reference I

£OUSl.A.s., ~.~.~enzO,LA.. Ck~mp,C.W. &laud.[. andAndersen.L.B [191~[h Princtpl(,~ (It L nlt CJi)t,tatt(m~~2nd ednJ. p. 8. [uhnWiley & Sor,s

Aseptic Processing of Foods edited bv H. Router,Technomie, 1993. Sw. Fr. 135.00 {313 pages,ISB,", I 36676 038 3

In recent years, aseptic processing has benefitted from many advances in the processing of loud products, using various types of heat exchange systems and packaging machines to handle a variely of products and packages under aseptic conditions. The heating of particulate materials with traditional heat exchangers {i.e. tubular, scraped-surface and steam infusion) is rather slow compared with that of liquid foods. The newer technologies such as ohmic resistance and dielectric heating methods have resulted in shorter sterilization times due to energy transiormalion inside the solid particles. Tim sections on ohmic resistance and dielectric heating, and on the processing oi particulatecontaining {nods present newer technologies to advance the state of the art in this area. In addition to in]proved processing techniques, a varieb ol advanced aseptic packaging systems have also been introduced to the food industry. These packaging machines offer great ile
Trends in Food Science& TechnologyFebruary 1994 [\'ol. ~!

packages (i.e. type, size, shape, etc,l. Also, the packaging machines haw~ been integrated with clean-room processing technology, which does not produce truly aseptic producls bul uses the same equipment as aseptic processing. Much of the information pre~ented is very useful for the continuous processing of pumpable products and is not limited only to aseptic processing. As noted by the editor, this hook is intended to su~.plement another book by the same editor, Aseptic £ack,rz4ing of Food ~, and each book is based on a separate symposium on this subjeci. Aseptic Processing of Foods meets its intended purpose, and vet has a wide coverage on various theoretical and practical aspects of both processing and packaging systems. The coraenls are laid out in a clear and logical ma~:ner. The book is an excellent source of information/or those interested in aseptic processing and packaging technology and ,.,.,ill definitely ~,erve as a reference book for iood processing professionals. It is also suitable for use

6:"

BookReviews as a text for post-baccalaureatecourses or industrial training programs. In addition the details of commercial processes and aseptic systems make it very attractive for use by food indust~' personnel. The maior strength of this book is the detailed descriptions of some commercial systems, which are rarely available in the published literature to academics and researchers. However, no index

nor detailed references are included in the book. Since the chapters are written by different authors, the book also lacks a consistent style, but the editor has done ~n excellent job in arranging and presenting such diverse information in an easy-to-follow format. 1 would strongly recommend that this book finds its way into re(erence libraries and onto the shelves of food processing pro-

Food Process Monitoring Systems ediled by A,C. Pinder and G. Godl'rey,Blackie, 1993. £65.00 (xii + 220 pages)ISBN0 7514 0099 8

In-line product quality monitoring presents difficulties in many sectors of the food industry, and it has long been recognized that progress in automatic control is dependenl on the development of sensors thai are sufficiently robust and stable to be used in a closed loop. The Food Processing Sciences LINK Programme, sponsored by the UK Department of Trade & Industry and Ministry of Agriculture, Fisheries and Foods, and some aspects of the parallel Agro-Food Quality LINK Programme have included various sensor development projects; most of the acknowledged sensor needs are being tackled somewhere within these wide-ranging programmes, and some success has been achieved. The first topic covered by the book, fluorescence cytometry for rapid analysis of microorganisms, is treated authoritatively by A. Pinder and S. Gatley; the latte[ is the only author from outside the UK. Fluorescent labelling techniques are particularly well covered. Fluorescent labels give optical cytometry a unique advantage: in instances where the emission spectra do not overlap, it is possible to measure several cell parameters simultaneously, The applications of cytometry for detecting yeast in fruit and in fermented milk products, for measuring the activity of starter cultures, and as a predictive tool for fruit and salad vegetable shelf life are described. Near-infrared (NIR) and more recemly mid-infrared (MIR) on-line sensors have been outstanding among the successful applications of new technology to food quality testing. The chapter

6B

by R.H, Wilson and E.K. Kemsley is notably informative. Moisture, lipid and protein absorption bands are all conveniently accessible in the NIR, and can be observed using well-tried optical arrangements. Coffee granules, milk powders, flour and extruded cereal products are routinely monitored in this way; where the material is a homogeneous powder, moisture content can be measured to within 0.1%. The technique deFunds on being able to view a freshly exposed and representative surface. MIR devices are less widespread than NIR ones due to practical problems with optics and detectors. Current MIR applications are restricted to attenuated total reflectance methods for fluids, where the beam is reflected to and fro within a crystal immersed in the fluid. Sugars in fruit juice cause an absorption at 3.4pro, which has been used to monitor sugar content to an accuracy of within 0.2%. For the future, deve!opment is progressing with Fourier transform infrared sensors, in which a laser beam is split in a configuration like a Michelson intefferometer, and the path length of one path is varied using an oscillating mirror. A scan of a small spectral region is completed for each half cycle of the mirror, and the detected signal decoded by Fourier transform. The use of a He-Ne laser makes the waveiangth scale sufficiently stable for multiple scans to be integrated, allowing data to be obtained from transmission through highly attenuating material. Vision systems are reviewed by J.P. Chan and B.G. Batchelor. There are many potential applications, bu~ so far

fessionals, even those working in areas beyond that of aseptic processing. Rakesh K. Singh Depa[~ments or' FoodScienceand Agricultural Engineering,PurdueUniversiry, WesrLafayelte. tN47907-~160, USA.

Reference I

Reuler,H., ed.{1989)AsepticPackagingof Food, lechnomic

few reported cases where image analysis is actually in use; consequently the chapter is mainly a catalogue of topics needing more investigation, but the examples do give a clear indication of what may be possible. Low angle laser light scattering has enabled greal progress 1o be made in equipment for particle sizing, and has found particular application in chocolate manufacture. A dispersion of particles is placed in an expanded beam, and a stationary diffraction pattern forms on a diode array. Work by Malvern Instruments Ltd has shown that the technique requires particles to be within a fairly narrow range of concentration, and decoding requires careful application of Fraunhofer and Mie scattering formulae. The chapters on ultrasonic methods and mass spectrometry are good technical summaries of each topic, but applications are few and highly specialized. This is not the case with chemical sensors, and, in the final chapter, E. KressRogers gives a brief but informative and well-balanced account of the ways in which various sensors, particularly solid-state pH sensors and gas sensor arrays, have been made sufficiently rugged for everyday use in testing a wide range of foods. This book provides a detailed review of progress in seven of the many areas of current interest, together ~,~th numerous well.chosen references. There is, however, no mention of colour measurement as such, nor of texture or rheology, nor of gas chromatography or nuclear magnetic resonance. The allimportant topic of moisture only gets a passing mention in the chapters on infrared spectroscopy and ultrasonic methods.

lan McFarlane 107 Hotspur Top Lane, Beaconsfield, Buckinghamshire, UK HP9 tDT.

Trends in FoodScience& TechnologyFebruary 1994 IVo~. 51