Ghani Al-Baali / Farid Sterilization of Food in Retort Pouches

1. Auflage 2007
ISBN: 978-0-387-31129-6
Verlag: Springer US
Format: PDF
Kopierschutz: 1 - PDF Watermark

E-Book, Englisch, 205 Seiten, eBook

Reihe: Food Engineering Series

Sterilization of canned food is a well-known technology that has been in practice for many decades. Food sterilization has been well studied in a large number of textbooks. This book is not about the science of sterilization or food safety but rather about the important interaction between ?uid mechanics, heat transfer, and microbial inactivation. Such interaction is complex and if ignored would lead to incorrect information not only on food sterility but also on food quality. The book is written by engineers for both food engineers and scientists. However, it may also be of interest to those working in computational ?uid dynamics (CFD). It presents an elementary treatment of the principles of heat transfer during thermal sterilization, and it contains suf?cient material presented at a high level of mathematics. A background in the solution of ordinary and partial differential equations is helpful for proper understanding of the main chapters of this book. However, we have avoided going into a detailed numerical analysis of the ?nite volume method (FVM) of solutions used to solve the sets of equations. Some familiarity with ?uid dynamics and heat transfer will also be helpful but not essential. Inthisbook,conductionandconvectiveheattransferistreatedsuchthatthereaderisofferedthe insight that is gained from analytical solutions as well as the important tools of numerical analysis, which must be used in practice. Analysis of free convection is used to present a physical picture of the convection process.

Zielgruppe

Research

Autoren/Hrsg.

Ghani Al-Baali, A.G. Abdul

Farid, Mohammed M.

Inhaltsverzeichnis

Thermal Sterilization Of Food.- Heat Transfer Principles.- Principles Of Thermal Sterilization.- Fundamentals Of Computational Fluid Dynamics.- Thermal Sterilization Of Food In Cans.- Theoretical Analysis Of Thermal Sterilization Of Food In 3-D Pouches.- Pouch Product Quality.- Experimental Measurements Of Thermal Sterilization Of Food In 3-D Pouches.- A New Computational Technique For The Estimation Of Sterilization Time In Canned Food.

Leseproben

CHAPTER 2 HEAT TRANSFER PRINCIPLES (p. 17-18)

Food preservation remains to be one of the important food processing industries. Early approaches to food preservation applied the methods of preservation naturally available, such as sun drying, salting, and fermentation, which were used to provide food in periods when fresh foods were not available. As civilization developed, demand for large quantities of better quality processed food also increased. This led to the development of a large food preservation industry aimed at supplying food of high quality in an economical way. Thermal sterilization of foods is the most signi.cant part of this industry (Karel et al., 1975). Other methods of sterilization such as a pulsed electric .eld (Barbosa-Canovas et al., 1998, Barbosa-Canovas and Zhang, 2000, Jia et al., 1999, Martin et al., 1997, Qin et al., 1994, 1998, Sepulveda-Ahumada et al., 2000, Vega-Mercado et al., 1997, 1999, Zhang et al., 1995), ultrahigh hydrostatic pressure (Barbosa-Canovas et al., 1997a, Furukawa and Hayakawa, 2000, Paloua et al., 1999, Sancho et al., 1999), and ultraviolet (UV) treatment (Farid et al., 2000) have been widely studied. However, with the exception of high-pressure processing, these technologies have not yet reached commercialization stage.

2.1. INTRODUCTION TO THERMAL STERILIZATION

Two different methods of conventional thermal processing are known: aseptic processing, in which the food product is sterilized prior to packaging, and canning in which the product is packed and then sterilized (Barbosa-Canovas et al., 1997b). Food after being canned has to undergo thermal treatment to deactivate most organisms (i.e. sterilization). In 1981, the food industry in the United States alone processed more than 16.3 billion kg of food products in approximately 37 billion containers (Kumar et al., 1990).

Thermal sterilization is one of the most effective means of preserving a large part of our food supply. The objective of sterilization is to extend the shelf life of food products and make the food safe for human consumption by destroying harmful microorganisms. A sterilizer is a unit in which food is heated at high temperature and then held at that temperature for a period suf.cient to kill the microorganisms of concern from the foodproduct. A sterile product is one in which no viable microorganisms are present. A viable organism is one that is able to reproduce when exposed to conditions that are optimum for its growth. Temperature slightly higher than the maximum for bacterial growth results in the death of vegetative bacterial cells, whereas bacterial spores can survive at much higher temperatures. Since bacterial spores are far more heat resistant than vegetative cells, they are of primary concern in most sterilization processes. Saturated steam is the most commonly used and highly desirable heating medium for commercial sterilization of canned foods. Conventional canning consists of the following operations:

1. Preparing the food (cleaning, cutting, grading, blanching, etc.)
2. Filling the container
3. Sealing the container
4. Placing the container in a batch or continuous retort where it is heated for a time sufficient for commercial sterility
5. Cooling of the container, which is usually done using a cold shower

The still retort is the oldest type of equipment used for thermal processing. It is still used in large canning plants for metal- and glass-packed products. The sterilization method using a still retort consists of loading the containers, which are placed into baskets immediately after seaming and then into an appropriately designed iron vessel (retort), closing the vessel, and heating the containers with steam. A controller regulates the temperature, and the duration of heating is determined by the rate of heat transfer into the containers. Introduction of steam into the retort should be done with care since it is necessary to displace all of the air in the retort. The presence of air during thermal sterilization processing can result in under-processing since steam–air mixtures result in lower heat transfer rates (Karel et al., 1975).