Innovative Technologies for Food Preservation

Inactivation of Spoilage and Pathogenic Microorganisms

Francisco J. Barba, Anderson de Souza Sant'Ana, Vibeke Orlien, Mohamed Koubaa

• Publisher: Academic Press
• Year: 2017
• Print ISBN: 9780128110317
• eBook ISBN: 9780128110324
• Topic: Technology & Engineering
• Subtopic: Food Science
• Index: Technology & Engineering

Innovative Technologies for Food Preservation: Inactivation of Spoilage and Pathogenic Microorganisms covers the latest advances in non-thermal processing, including mechanical processes (such as high pressure processing, high pressure homogenization, high hydrodynamic pressure processing, pressurized fluids); electromagnetic technologies (like pulsed electric fields, high voltage electrical discharges, Ohmic heating, chemical electrolysis, microwaves, radiofrequency, cold plasma, UV-light); acoustic technologies (ultrasound, shockwaves); innovative chemical processing technologies (ozone, chlorine dioxide, electrolysis, oxidized water) and others like membrane filtration and dense phase CO2. The title also focuses on understanding the effects of such processing technologies on inactivation of the most relevant pathogenic and spoilage microorganisms to ensure food safety and stability.Over the course of the 20th century, the interest and demand for the development and application of new food preservation methods has increased significantly. The research in the last 50 years has produced various innovative food processing technologies and the use of new technologies for inactivation of spoilage and/or pathogenic microorganisms will depend on several factors. At this stage of development there is a need to better understand the mechanisms that govern microbial inactivation as induced by new and innovative processing technologies, as well as suitable and effective conditions for inactivating the microorganism.- Serves as a summary of relevant spoilage and pathogenic microorganisms for different foods as influenced by the application of innovative technologies for their preservation- Provides readers with an in-depth understanding on how effective innovative processing technologies are for controlling spoilage and pathogenic microorganisms in different foods- Integrates concepts in order to find the optimum conditions for microbial inactivation and preservation of major and minor food compounds

Part I

Introduction

Outline

Chapter 1 Conventional Technologies of Food Preservation

Chapter 2 Innovative Technologies for Food Preservation

Chapter 3 Main Groups of Microorganisms of Relevance for Food Safety and Stability: General Aspects and Overall Description

Chapter 1

Conventional Technologies of Food Preservation

Pedro E.D. Augusto¹, Beatriz M.C. Soares² and Nanci Castanha¹, ¹University of São Paulo (USP), Piracicaba, SP, Brazil, ²Food Technology Institute (ITAL), Campinas, SP, Brazil

Abstract

The food microbiological stability is achieved by the reduction of the initial microbial load using a suitable procedure (generally a thermal process) followed by maintaining the residual microbial load to acceptable levels.

The factors that affect microbial growth are generally classified into two groups: intrinsic (i.e., of the food) and extrinsic (i.e., of the environment) factors. The main intrinsic factors of food are its water activity (a_w), pH and acidity, redox potential (Eh), and the nutrient content. The main extrinsic factors are the temperature and atmospheric composition. The microbial growth will therefore be faster or slower depending on the composition of these factors in relation to the microbial requirements.

Therefore, understanding the factors that affect microbial inactivation and growth is essential to guarantee safe and stable products.

This chapter describes the main conventional technologies for food preservation, as well as their combination through the hurdle technology.

Keywords

Preservation; food preservation; conventional methods; conventional technologies; traditional technologies; food processing

1.1 Thermal Processing

The thermal process is one of the most widely used methods for food preservation, even considering its drawbacks and the development of further nonthermal technologies. It is a unit operation where the food is heated to a certain temperature, maintained for a certain time in order to promote the required microbial and/or enzymatic inactivation, and then cooled. It is generally characterized by a (applied) binomial time and process temperature (t×T), or, even better, an equivalent time at a specific temperature (for example through the F value concept).

The food preservation by thermal processing is based on the use of thermal energy (heat) for microbial and enzymatic inactivation, obtained due to protein denaturation and melting of lipid components, among other effects. However, although microbial and enzymatic inactivation is desirable, the thermal processing also results in other reactions (generally) undesirable, such as sensorial changes and nutrient destruction. The challenge, therefore, is to guarantee a safe and stable product (with the desired microbial and enzymatic inactivation), but with better sensorial and nutritional properties, with lower costs and energy saving consumption.

During processing, the food is heated by a hot fluid to the process temperature, following the heat transfer mechanisms. The food is then kept at this temperature for a certain time, previously calculated in order to optimize the product characteristics (i.e., safety assurance with better sensorial and nutritional attributes), called processing time. The food is then cooled by a cold fluid, interrupting the thermal effects.

The thermal processing is designed based on the process target, i.e., the most thermal-resistant undesirable microorganism or enzyme in the food product. The thermal process design will thus be calculated based on this target, ensuring safety and quality of the processed food.

The thermal process target can be a vegetative cell (as in beer or milk pasteurization), a microbial spore (as in the sterilization processes of low-acid foods—such as milk, corn, and tuna), a microbial toxin (as in the pasteurization of palm heart), or an enzyme (as some resistant pectinolytic enzymes in fruit products). The process target must be chosen aiming firstly food safety, but also considering the nutritional and sensorial characteristics of the final product and the economics.

1.1.1 Thermal Processing Main Characteristics

The main thermal processes used in food preservation are commonly described as commercial sterilization (usually referred as, simply, sterilization) and pasteurization.

The commercial sterilization is a more drastic thermal process, where the final product should have no vegetative cells and spores capable of growing under normal conditions of transportation and storage (Codex Alimentarius, 2003). Thus, in addition to safety, it is a process that ensures stability at ambient conditions (in general for periods in the order of months to some years).

It is a preserving method widely applied to low-acid foods such as milk, meat, corn, peas, carrots, and other vegetables that may be contaminated with spores of Clostridium botulinum, which represent a potential risk to the safety of the product and must be inactivated. Sterilized food is generally processed in pressurized systems, at temperatures of about 120–150°C for an appropriate time. The sterilized products show high stability and shelf life from months up to years. In this case, the final shelf life of the product is determined by physico-chemical and/or sensorial changes.

Pasteurization is a milder thermal process, whose main objectives are to ensure safety and prolong food shelf life. It is a method that needs to be used with a complementary technology (such as cooling, acidification, reduction of water activity, and/or use of preservatives) to guarantee stability. It is generally carried out under atmospheric pressure, with temperatures of about 65–100°C for an appropriate time.

Pasteurization is a process widely applied for the preservation of fruit juices, milks, fermented drinks, heart of palm, and other preserves, and its use implies the need for association with another preservation method. Pasteurized products have low to medium stability and variable shelf life, according to their characteristics and complementary conservation method. Their shelf life may vary from few days (as refrigerated pasteurized milk and other low-acid products with high a_w) up to months or years (as juices and fruit jams and other high-acid products and/or with low a_w).

Furthermore, the thermal processing of food can be performed inside or outside the package (Table 1.1).

Table 1.1

Main Characteristics of Food Thermal Processing Inside and Outside the Packaging

Processing Inside the Packaging	Processing Outside the Packaging
Solid, liquid, or particulate food	Liquid food (consistency/viscosity limitations) and, in some cases, particulates
Higher food safety	Filling process can compromise food safety
Lesser energy efficiency	Greater energy efficiency
Packaging must resist the process	Packaging must be previously sterilized
Final product with more changes and lesser homogeneity	More homogeneous final product with less physico-chemical and sensory changes

The in-package process is conducted with the product inside the packaging, i.e., the food is packaged in a hermetic package/container and then the product-packaging system is processed. In this way, the product does not come into contact with the environment after thermal processing (i.e., after the microbial inactivation). It is important to note that in this case, the packaging used must be resistant to the process conditions (temperature and pressure) to avoid deformations that compromise it. The thermal processing inside the packaging is often called Appertization, in honor of Nicolas Appert, a French confectioner who developed methods to preserve packaged foods due to thermal processing, winning a prize in 1810 stipulated by Napoleon Bonaparte for the development of a more efficient conservation method.

In the in-package thermal processes, a heating fluid is normally used and the heat is transferred to the packaging, then through the packaging, then from the packaging to the product, and finally across the product. After heating the product, it is maintained at the process temperature for a specified time and then being cooled. As the heat transfer is not instantaneous, each portion of food will have a different thermal history (T=f(t)) throughout the process. In this case, the process must be dimensioned for the region that the process resulted in a less lethal effect called cold spot or slower heating region (Fig. 1.1). In solid foods (conductive heating), the cold spot is typically located in the geometric center region of the product (for symmetrical packaging, for example, in the center of a cylindrical package). In liquid foods (convective heating), due to the natural convection currents formed during the process, such location is more complex, depending on several factors of the package and process (for example, the uniformity of heating) and product (mainly the rheological properties). However, it is in the lower portion of the packaging, generally between 10% and 20% of the height of a cylindrical package. In those cases, therefore, the guarantee of a safe product (process scaled to the cold spot) will result in regions with s...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of Contributors
• Part I: Introduction
• Part II: Microbial Inactivation After Innovative Processing of the Main Groups of Microorganism of Relevance for Food Safety and Stability
• Part III: Consumer’s, Technological, Environmental and Regulatory Aspects of Application of Emerging Technologies for Food Preservation
• Index