Use of physico-chemical methods for assessment of sensory changes in carrot texture and sweetness during cooking

The change in texture and flavour during cooking of carrot discs of 5 different batches was investigated by sensory analysis and four different physicochemical measurements. The five most important sensory attributes were sweet odour, sweet taste, juiciness, hardness and crispness. All sensory descriptors underwent a similar decrease in intensity during cooking for up to 15 min. Hardness and crispness were highly correlated. Principal Component Analysis (PCA) showed differences between the experimental samples. The first principal component explained 99% of the total variance and was related to the cooking time. The second principal component pointed at differences between the carrot batches, for example, carrots grown on a sandy soil (3-4% organic matter) and kept over winter on a straw covered field, were less sweet, but more juicy, crisp and hard than carrots of the same cultivar grown on a soil with a higher humus content (8% organic matter) and kept in a cool store. Soluble solids content (SSC), dry matter (DM), tensile strength (F) and compressive strength (F) also decreased with cooking time. SSC and DM decreased more or less linearly, while F, and F c showed an exponential decrease from one minute cooking onwards. Due to the different effect of cellular turgor on tensile and compressive strength, F t dropped rapidly within the first minute of cooking, while F c remained constant. F t and F c showed a high correlation with the sensory parameters. A two-component PLS-model including all four physico-chemical measurements estimated the juiciness with an average root mean square error of prediction (RMSEP) of 0.25 on a sensory scale ranging from 0 to 15, and the other attributes with an average RMSEP between 1 and 1.25. These physico-chemical measurements provide a faster and cheaper quality estimation than sensory evaluation by a trained panel and may help the ready-to-use food products and catering industries to determine optimum cooking times.