Influence of Water on Prediction of Composition and Quality Factors: The Aquaphotomics of Low Moisture Agricultural Materials

Abstract

The main constituents of agricultural materials are starch, protein, oil (lipid), cellulose and minerals. These constituents all exist in the molecular state and are constantly in motion, but are essentially functionally static in the raw materials from which foods and feeds are made. It is only when the molecules are brought together by an external medium that brings them into contact with each other in a way in which they can interact more freely, that the molecules are able to create new products. The most important medium is water. Water has a profound influence on the behaviour and the spectra of agricultural commodities. The paper will demonstrate that during the development of near infrared (NIR) calibration models, using several different approaches, the selection of wavelengths in areas where water is known to absorb in the NIR region, is widespread among calibrations for prediction of composition, and functionality in systems in which the moisture content is not high (up to about 15% moisture), and water is not the dominant constituent. Over 200 references have been made to assignments for water in some form, between 700–2200 nm. The influence of water on NIR calibration models for prediction of composition and functionality of materials of even fairly low moisture content is convincing. Evidence is presented in terms of partial least squares loadings for NIR calibration models developed on these materials. The relevance of this is discussed with respect to the possibility of interaction with other absorbers at the same, or adjacent wavelengths. The concept is presented that studies of changes in the intensity and positions of the absorbances of water, and those of other major constituents during development of NIR calibration models, can provide new information on the interaction among these constituents that result in differences in the structure and functionality of the materials, and on the efficiency of NIR analysis.