The effect of pH in the range 5.0 to 7.0 on the thermal destruction of spores of Clostridium sporogenes putrefactive anaerobe 3679 was examined by three methods: a capillary tube method in which spores were suspended in phosphate buffers, a thermoresistometer method in which spores were suspended in buffered pea puree adjusted to the same set of pH values, and a thermal death time can method in which spores were again suspended in buffered pea puree. The results indicated that increasing acidity is, in general, accompanied by decreasing heat resistance, although the pH effect was more pronounced at the higher than at the lower processing temperatures. Certain pH values appear to be critical, as they produced, in all three sets of experiments, effects which would not be predicted by the overall relationship between acidity and spore heat resistance. Differences between heat resistance in phosphate buffer as compared with that in pea puree adjusted to the same pH were also noted. D-values in buffer were found to be lower than those in pea puree, except at the highest temperatures coupled with the lowest pH values. The differences between buffer D-value and pea puree Dvalue were found to increase with increasing pH and with decreasing temperature. On the other hand, at all pH values examined, z-values determined in buffer were somewhat higher than those determined in pea puree adjusted to the same pH.

No abstract

Concentrated tomato products require dilution to 12% natural tomato soluble solids ( N T S S ) before consistency can be determined using the Bostwick consistometer. The data show that the measured value is dependent upon the amount of added water required to reach the specified solids content. The extent of desiccation of the water insoluble fraction of the solids and their inability to resorb maximally is proposed as the cause of the phenomenon. Heating is suggested as a n additional step in the determination of consistency of tomato products to reduce the error caused by inefficient resorption of water at ambient temperatures.Consistency is not considered a mandatory quality attribute of the concentrated product, tomato paste. However, lately it has assumed an economic importance as more of this product is used on a re-manufacturing

Two general types of pectic enzymes are involved in the breakdown of pectic materials : pectin esterase (PE) , which splits the methyl ester linkages in pectinic acid or pectin to yield pectic acid, and polygalacturonase (Pa), which hydrolyzes the 1,4-alpha-glycosidic bonds i n the uronide chain to yield galacturonic acid. The existence of more than one kind of polygalacturonase has received increased attention in recent years (1, 2, 3, 12, 20, 22, 23, 24).Pectin-degrading enzymes in tomatoes have been studied by several workers (10, 11, 12, 13, 14, 19, 21). McColloch and Kertesz (13) reported that the maximum increase in reducing value of pectic acid acted upon by tomato depolymerase is about 50% of the theoretically possible value. It is difficult, however, to correlate the presumed end-product of the reaction a t 50% hydrolysis, a postulated pentamer of galacturonic acid, with such a high percentage of glycosidic hydrolysis.Roelofsen (21) reported that crude tomato extract does not contain a pectic acid depolymerase, but a polygalacturonase able to split pectic acid into a mixture of mono-, di-, and trigalacturonic acids. The most recent work on this enzyme by McCready, McComb, and Jansen (14) shows that tomato P G can hydrolyze pectic acid completely to galacturonic acid. In this respect, it is qualitatively similar to purified fungal PG, although quantitatively the tomato enzyme showed a slower rate of digalacturonie acid hydrolysis than the fungal enzyme. In view of recent interest in the nature and complexity of polygalacturonase from different sources, and the important role which pectic enzymes play i n the consistency of macerated tomato products, we have investigated the viscometric changes of pectic acid and the rate, degree, and products of hydrolysis of pectic acid by pectic enzyme preparations from Pearson or San Marzano tomatoes. In addition, the action of a partially purified tomato P G on di-, tri-, and tetragalacturonic acids was also studied.

The change in Bostwick consistency of tomato juice with change in solids during concentration was found to be related to the waterinsoluble solids @!JIS):total solids (TS) ratio and to the viscosity of the serum of clarified juice. These characteristics were found to be widely variable among new tomato cultivars. The slope of the concentration curve was found to be primarily dependent upon the WlS/TS ratio. The locus of the concentration curve, on the other hand, was found to be dependent on both WIS/TS ratio and serum viscosity, and could be located by Bostwick consistency of the juice and initial solids content. The influence of these characteristics on processing and Bostwick consistency of tomato paste is discussed.