Formation of 5-hydroxymethylfurfural in industrial-scale apple juice concentrate processing

In industrial-scale apple juice concentrate (AJC) processing, 5-hydroxymethylfurfural (5-HMF or 5-(hydroxymethyl)-2-furaldehyde) is a furanic compound that is formed as an intermediate under certain conditions during thermal treatments applied to foods, especially AJC. Understanding 5-HMF formation is significant, particularly because 5-HMF is undesirable in foods due to its harm to humans’ health, but its presence and content is also an indicator of the processing technique used to prepare the food. The aim of this study was to investigate the changes in 5-HMF and other physicochemical indicators during AJC processing, and to critically analyse the impacts of those physicochemical indicators on the generation of 5-HMF. In this study, 5-HMF content, conventional physicochemical parameters, two monosaccharides, one disaccharide, 18 amino acids, and 12 polyphenols were monitored during 8 crucial stages of AJC production. 5-HMF formed primarily during three thermal processing stages: preconcentration, enzymatic clarification, and quintuple effect concentration. Color value increased, and brown index decreased significantly during processing. Fructose and glucose were the most abundant saccharides present in apple juice. Asparagine and aspartic acid were the two highest contents of amino acids detected, and amino acids contents showed little variation after the resin decolorization stage. Phloridzin content was highest in the original apple fruit, but all polyphenols showed significant variability during processing, especially during adsorption after the resin decolorization stage. The formation of 5-HMF showed a positive correlation with soluble solids content, color value, total sugar, fructose, glucose, glutamic acid, asparagine, threonine, alanine, methionine, proline, gallic acid, and rutin content. The formation of 5-HMF is dependent upon the fructose, glucose and specific amino acids content under acidic and thermal conditions found in industrial-scale AJC processing. Understanding the factors influencing 5-HMF formation can help to control its formation in AJC processing.