Nondestructive optical methods of food quality evaluation

Quality control is an important aspect of food production and processing from the point of view of providing foods of acceptable nutritional value, and for providing safety of products. Several characteristics such as size, shape, density, maturity, moisture content, oil content, flavor, firmness, tenderness, color, defects, blemishes, etc., are routinely used in the quality control of agricultural and biological food products. Until recently, most analytical techniques used in quality control required isolation of the food component of interest. The original properties of the product are, therefore, destroyed during sample preparation and analysis. Oftentimes, such analyses are expensive, time consuming, and require sophisticated instrumentation, and hence are not suited for "on-line" quality control of food products. Recent progress in the development of instrumentation utilizing the optical properties of food products has provided several nondestructive techniques for quality evaluation. Most optical methods of nondestructive nature make use of the characteristic absorption spectra of components of interest. Such methods are highly sensitive, rapid, and reproducible, and have been successively used in routine "on-line" quality control of a large number of samples. In this article, theoretical considerations in the development of nondestructive analytical techniques based on the optical properties of several agricultural and biological products are briefly reviewed. A major emphasis is placed on quality control methods that are particularly useful in maturity and/or ripeness evaluation of food products, the detection of external and internal defects, and the subsequent development of automatic sorting machines for on-line measurement of quality.