Hardness Methods for Testing Maize Kernels

Abstract

Maize is a highly important crop to many countries around the world, through the sale of the maize crop to domestic processors and subsequent production of maize products and also provides a staple food to subsistance farms in undeveloped countries. In many countries, there have been long-term research efforts to develop a suitable hardness method that could assist the maize industry in improving efficiency in processing as well as possibly providing a quality specification for maize growers, which could attract a premium. This paper focuses specifically on hardness and reviews a number of methodologies as well as important biochemical aspects of maize that contribute to maize hardness used internationally. Numerous foods are produced from maize, and hardness has been described as having an impact on food quality. However, the basis of hardness and measurement of hardness are very general and would apply to any use of maize from any country. From the published literature, it would appear that one of the simpler methods used to measure hardness is a grinding step followed by a sieving step, using multiple sieve sizes. This would allow the range in hardness within a sample as well as average particle size and/or coarse/fine ratio to be calculated. Any of these parameters could easily be used as reference values for the development of near-infrared (NIR) spectroscopy calibrations. The development of precise NIR calibrations will provide an excellent tool for breeders, handlers, and processors to deliver specific cultivars in the case of growers and bulk loads in the case of handlers, thereby ensuring the most efficient use of maize by domestic and international processors. This paper also considers previous research describing the biochemical aspects of maize that have been related to maize hardness. Both starch and protein affect hardness, with most research focusing on the storage proteins (zeins). Both the content and composition of the zein fractions affect hardness. Genotypes and growing environment influence the final protein and starch content and, to a lesser extent, composition. However, hardness is a highly heritable trait and, hence, when a desirable level of hardness is finally agreed upon, the breeders will quickly be able to produce material with the hardness levels required by the industry.

Milhos com diferentes texturas de endosperma e adição de alfa-amilase na dieta de leitões

“…A dureza é uma característica física que influencia na qualidade e no processamento dos grãos de milhos e a vitreosidade é uma medida indireta da dureza do grão (FOX & MANLEY, 2009). A proporção de endosperma vítreo em relação ao endosperma total, obtida por dissecação dos grãos, também é denominada de vitreosidade (PHILIPPEAU & DOREAU, 1998;CORREA et al, 2002).…”

Determination of maize kernel hardness: comparison of different laboratory tests to predict dry-milling performance

“…The maize physical characteristics, kernel size and shape, weight and density, resistance to grinding or to abrasion and quantification of coarse and fine material after grinding and sieving have all been linked to hardness and its subsequent effects on processing. 11 Other indirect available tests to estimate maize hardness are based on the viscosity of the ground material (Rapid ViscoAnalyser) 13 or on near-infrared reflectance (NIR) and transmittance (NIT), both of which use whole kernels or kernels after the grinding step.…”

A Review of Optical Nondestructive Visual and Near-Infrared Methods for Food Quality and Safety

“…For maize, the hardness was evaluated using NIR spectra in [97]. Manley et al [98] used hyperspectral images of 1000 to 2498 nm wavelength range to classify yellow maize kernels.…”