Food Processing Handbook

James G. Brennan, Alistair S. Grandison, James G. Brennan, Alistair S. Grandison

• Editore: Wiley-VCH
• Anno: 2012
• ISBN:
  9783527634378
• Edizione: 2
• Argomento: Technology & Engineering
• Categoria: Food Science

The second edition of the Food Processing Handbook presents a comprehensive review of technologies, procedures and innovations in food
processing, stressing topics vital to the food industry today and pinpointing the trends in future research and development. Focusing on the technology involved, this handbook describes the principles and the equipment used as well as the changes - physical,
chemical, microbiological and organoleptic - that occur during food preservation. In so doing, the text covers in detail such techniques as
post-harvest handling, thermal processing, evaporation and dehydration, freezing, irradiation, high-pressure processing, emerging technologies and packaging. Separation and conversion operations widely used in the food industry are also covered as are the processes of baking, extrusion and frying. In addition, it addresses current concerns about the safety of processed foods (including HACCP systems, traceability and hygienic design of plant) and control of food processes, as well as the impact of processing on the environment, water and waste treatment, lean manufacturing and the roles of nanotechnology and fermentation in food processing. This two-volume set is a must-have for scientists and engineers involved in food manufacture, research and development in both industry
and academia, as well as students of food-related topics at undergraduate and postgraduate levels. From Reviews on the First Edition:
"This work should become a standard text for students of food technology, and is worthy of a place on the bookshelf of anybody involved in the production of foods."
Journal of Dairy Technology, August 2008 "This work will serve well as an excellent course resource or reference as it has well-written explanations for those new to the field and detailed equations for those needing greater depth."
CHOICE, September 2006

Volume 1

1

Postharvest Handling and Preparation of Foods for Processing

Alistair S. Grandison

1.1 Introduction

Food processing is seasonal in nature, both in terms of demand for products and availability of raw materials. Most crops have well-established harvest times – for example, the sugar beet season lasts for only a few months of the year in the United Kingdom, so beet sugar production is confined to the autumn and winter, yet demand for sugar is continuous throughout the year. Even in the case of raw materials that are available throughout the year, such as milk, there are established peaks and troughs in volume of production, as well as variations in chemical composition. Availability may also be determined by less predictable factors, such as weather conditions, which may affect yields or limit harvesting. In other cases demand is seasonal, for example, ice cream or salads are in greater demand in the summer, whereas other foods are traditionally eaten in the winter months, or even at more specific times, such as Christmas or Easter.

In an ideal world, food processors would like a continuous supply of raw materials, whose composition and quality are constant and whose prices are predictable. Of course this is usually impossible to achieve. In practice, processors contract ahead with growers to synchronize their needs with raw material production.

The aim of this chapter is to consider the properties of raw materials in relation to food processing, and to summarize important aspects of handling, transport, storage, and preparation of raw materials prior to the range of processing operations described in the remainder of this book. The bulk of the chapter will deal with solid agricultural products including fruits, vegetables, cereals, and legumes, although many considerations can also be applied to animal-based materials such as meat, eggs, and milk.

1.2 Properties of Raw Food Materials and their Susceptibility to Deterioration and Damage

The selection of raw materials is a vital consideration to the quality of processed products. The quality of raw materials can rarely be improved during processing, and while sorting and grading operations can aid by removing oversize, undersize, or poor-quality units, it is vital to procure materials whose properties most closely match the requirements of the process. Quality is a wide-ranging concept and is determined by many factors. It is a composite of those physical and chemical properties of the material which govern its acceptability to the “user.” The latter may be the final consumer, or more likely in this case, the food processor. Geometric properties, color, flavor, texture, nutritive value, and freedom from defects are the major properties likely to determine quality.

An initial consideration is selection of the most suitable cultivars in the case of plant foods (or breeds in the case of animal products). Other preharvest factors (such as soil conditions, climate, and agricultural practices), harvesting methods and postharvest conditions, maturity, storage, and postharvest handling also determine quality. These considerations, including seed supply and many aspects of crop production, are frequently controlled by the processor or even the retailer.

The timing and method of harvesting are determinants of product quality. Manual labor is expensive, therefore mechanized harvesting is introduced where possible. Cultivars most suitable for mechanized harvesting should mature evenly, producing units of nearly equal size that are resistant to mechanical damage. In some instances, the growth habits of plants (e.g., pea vines, fruit trees) have been developed to meet the needs of mechanical harvesting equipment. Uniform maturity is desirable as the presence of over-mature units is associated with high waste, product damage, and high microbial loads, while under-maturity is associated with poor yield, lack of flavor and color, and hard texture. For economic reasons, harvesting is almost always a “once over” exercise, hence it is important that all units reach maturity at the same time. The prediction of maturity is necessary to coordinate harvesting with processors' needs, as well as to extend the harvest season. It can be achieved primarily from knowledge of the growth properties of the crop combined with records and experience of local climatic conditions.

The “heat unit system,” first described by Seaton [1] for peas and beans, can be applied to give a more accurate estimate of harvest date from sowing date in any year. This system is based on the premise that growth temperature is the overriding determinant of crop growth. A base temperature, below which no growth occurs, is assumed, and the mean temperature of each day through the growing period is recorded. By summing the daily mean temperatures minus base temperatures on days where mean temperature exceeds base temperature, the number of “accumulated heat units” can be calculated. By comparing this with the known growth data for the particular cultivar, an accurate prediction of harvest date can be computed. In addition, by allowing fixed numbers of accumulated heat units between sowings, the harvest season can be spread, so that individual fields may be harvested at peak maturity. Sowing plans and harvest date are determined by negotiation between the growers and the processors, and the latter may even provide the equipment and labor for harvesting and transport to the factory.

An important consideration for processed foods is that it is the quality of the processed product, rather than the raw material, that is important. For minimally processed foods, such as those subjected to modified atmospheres, low dose irradiation, mild heat treatment, or some chemical preservatives, the characteristics of the raw material are a good guide to the quality of the product. For more severe processing, including heat preservation, drying, or freezing, the quality characteristics may change markedly during processing. Hence, those raw materials which are preferred for fresh consumption may not be most appropriate for processing. For example, succulent peaches with delicate flavor may be less suitable for canning than harder, less flavorsome cultivars, which can withstand rigorous processing conditions. Similarly, ripe, healthy, well-colored fruit may be perfect for fresh sale, but may not be suitable for freezing due to excessive drip loss while thawing. For example, Maestrelli [2] reported that different strawberry cultivars with similar excellent characteristics for fresh consumption, exhibited a wide range of drip loss (between 8 and 38%), and hence would be of widely different value for the frozen food industry.

1.2.1 Raw Material Properties

The main raw material properties of importance to the processor are geometry, color, texture, functional properties, and flavor.

1.2.1.1 Geometric Properties

Food units of regular geometry are much easier to handle and are better suited to high-speed mechanized operations. In addition, the more uniform the geometry of raw materials, the less rejection and waste will be produced during preparation operations such as peeling, trimming, and slicing. For example, potatoes of smooth shape with few and shallow eyes are much easier to peel and wash mechanically than irregular units. Smooth-skinned fruits and vegetables are much easier to clean and are less likely to harbor insects or fungi than ribbed or irregular units.

Agricultural products do not come in regular shapes and exact sizes. Size and shape are inseparable, but are very difficult to define mathematically in solid food materials. Geometry is, however, vital to packaging and controlling fill-in weights. It may, for example, be important to determine how much mass or how many units may be filled into a square box or cylindrical can. This would require a vast number of measurements to perform exactly, and thus approximations must be made. Size and shape are also important to heat processing and freezing, as they will determine the rate and extent of heat transfer within food units. Mohsenin [3] describes numerous approaches by which the size and shape of irregular food units may be defined. These include the development of statistical techniques based on a limited number of measurements and more subjective approaches involving visual comparison of units to charted standards. Uniformity of size and shape is also important to most operations and processes. Process control to give accurately and uniformly treated products is always simpler with more uniform materials. For example, it is essential that wheat kernel size is uniform for flour milling.

Specific surface (area/mass) may be an important expression of geometry, especially when considering surface phenomena, such as the economics of fruit peeling, or surface processes such as smoking and brining.

The presence of geometric defects, such as projections and depressions, complicate any attempt to quantify the geometry of raw materials, as well as presenting processors with cleaning and handling problems, and yield loss. Selection of cultivars with the minimum defect level is advisable.

There are two approaches to securing optimum geometric characteristics: first, the selection of appropriate varieties, and second, sorting and grading operations.

1.2.1.2 Color

Color and color uniformity are vital components of the visual quality of fresh foods, and play a major role in consumer choice. However, it may be less important in raw materials for processing. For low-temperature processes, such as chilling, freezing, or freeze drying, the color changes little during processing, and thus the color of the raw material is a good guide to suitability for processing. For more severe processing, the color may change markedly during the process. Green vegetables such as peas, spinach, or green beans change color on heating from bright green to a dull olive green. This is due to the conversion of chlorophyll to pheophytin. It is possible to protect against this by addition of sodium bicarbonate to the cooking water, which raises the pH. However, this may cause softening of texture, and the use of added colorants may be a more practical solution....