Enzymes that convert starch and dextrins to alpha,alpha-trehalose and glucose were found in cell homogenates of the hyperthermophilic acidophilic archaeon Sulfolobus shibatae DMS 5389. Three enzymes were purified and characterized. The first, the S. shibatae trehalosyl dextrin-forming enzyme (SsTDFE), transformed starch and dextrins to the corresponding trehalosyl derivatives with an intramolecular transglycosylation process that converted the glucosidic linkage at the reducing end from alpha-1,4 to alpha-1,1. The second, the S. shibatae trehalose-forming enzyme (SsTFE), hydrolyzed the alpha-1,4 linkage adjacent to the alpha-1,1 bond of trehalosyl dextrins, forming trehalose and lower molecular weight dextrins. These two enzymes had molecular masses of 80 kDa and 65 kDa, respectively, and showed the highest activities at pH 4.5. The apparent optimal temperature for activity was 70 degrees C for SsTDFE and 85 degrees C for SsTFE. The third enzyme identified was an alpha-glycosidase (Ss alpha Gly), which catalyzed the hydrolysis of the alpha-1,4 glucosidic linkages in starch and dextrins, releasing glucose in a stepwise manner from the nonreducing end of the polysaccharide chain. The enzyme had a molecular mass of 313 kDa and showed the highest activity at pH 5.5 and at 85 degrees C.

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This study aimed to develop a low‐calorie apricot nectar by replacing sucrose with different amount of Stevia rebaudiana bertoni (Rebaudioside A, 98%). Stevia has become very popular as sweetener for the production of low‐calorie products but its addition could be a challenge for industry, since it could modify sensory features of the product and consumers' acceptance. To this end, apricot nectars without sugar, with sucrose 10%, and with different amounts of stevia were produced and evaluated for microbiological quality using the pour‐plate technique, and physicochemical (pH, TTA, and aw) and nutritional (moisture, fat, protein, carbohydrates, and ash) characteristics. Furthermore, a sensory analysis of the samples was performed by a panel of trained judges using quantitative descriptive analysis. The effect of stevia addiction on the consumers' acceptance was investigated by 102 consumers of fruit juices that evaluated the overall acceptability of the samples using a structured 9‐point hedonic scale. Levels of microbial groups in nectars were under the detection limit confirming a good hygienic practice within the production. Nectars produced with stevia resulted in significant reduction in caloric value from 86 kcal (nectar with 10% sucrose) to 49 kcal (nectars with stevia), without altering its typicality. Different sensory profiles among samples were pointed out; all the products are liked, but with a different level of pleasantness. The study highlighted that the apricot nectars with 0.07% stevia are characterized for sweet and liquorice aroma notes and received the same level of consumer acceptability of nectars produced with 10% sucrose.