EFFECT OF CRYOPROTECTANT MIXTURES ON RHEOLOGICAL PROPERTIES OF FRESH AND FROZEN/THAWED MASHED POTATOES

Abstract

ABSTRACT Hydrocolloids and protein were added to fresh (F) and frozen/thawed (F/T) mashed potatoes in the form of mixtures of: (1) amidated low‐methoxyl (ALM) pectin and xanthan gum (XG); (2) kappa‐carrageenan (k‐C) and XG; and (3) sodium caseinate (SC) and XG. F and F/T mashed potatoes without added biopolymers and with XG at 1.5 g/kg were also analyzed. Flow curves fit the power law and Casson models well – and preferentially the first of these. The Cox–Merz rule was not applicable to the steady and dynamic shear data on all of the mashed potatoes. In the F products, the departure of mashed potatoes–biopolymer mixtures from the Cox–Merz rule was XG concentration‐dependent. It was concluded that most of the F mashed potatoes followed the linear modified Cox–Merz rule, with η*(ω) and ηa() well superimposed. However, after processing, the linearity – or otherwise of the relationship between viscosities – was more dependent on the type of biopolymer mixture. Also, in the case of the F/T mashed potatoes without added biopolymers and with added ALM/XG binary mixtures, the relationships may be considered linear. Conversely, in the case of F/T mashed potatoes with added XG alone and mixed with k‐C and SC, small amplitude dynamic properties cannot be used directly to predict changes in texture perceived in the mouth given that the relationship between these properties and steady shear measurements is nonlinear. The effects of addition of either XG alone or binary mixtures to F and F/T mashed potatoes were very dependent on the magnitude of the strain deformation applied to the system (i.e., low strain in oscillatory shear and high strain in steady shear).PRACTICAL APPLICATIONSMashed potato can be a suitable food for freezing as a ready‐meal component or as a single product in the form of potato gratin. Freezing and thawing processes reduce most of the quality parameters measured in the product. One way of minimizing damage from freezing and thawing is to incorporate cryoprotectants to alter crystal shapes. Previous studies have shown that xanthan gum (XG) is preferred for sensory purposes because of its creamy mouthfeel. The result of this study could serve as a guide for thickening of mashed potatoes by addition of a kappa‐carrageenan (k‐C)/XG blend, and also for softening of the product by addition of a sodium caseinate (SC)/XG mix together. These data have served as a resource in order to further explore the utilization of XG mixed with either k‐C or SC in developing commercially prepared frozen/thawed mashed potatoes.