A method for the evaluation of freeze‐thaw stability of starch gels is described and compared with refrigerated‐storage retrogradation. Differential scanning calorimetry (DSC) is used to estimate the energy required to break down recrystallized starch molecules after 10 cycles of freezing‐thawing or after storage at 4°C for 1 week. Different DSC properties were observed for different starches. Chemical modification decreased all DSC values for gelatinization except the gelatinization range of all modified starches examined. Rice and wheat starches displayed the lowest energies of gelatinization compared with other native starches studied. Most chemical modifications completely inhibited the recrystallization of starches during storage at 4°C or after 10 cycles of freeze‐thaw. Mira‐Cleer 340® (modified regular maize starch; hydroxypropyl distarch phosphate) had a slight recrystallization value. DSC endotherms for both recrystallization studies occured at considerably lower temperatures than those of the original gelatinization.

Starch of high purity was isolated by a simple procedure from tepary beans (Phaseolus acutifolius var. latifolius). Granules were spherical to oval with a birefringence pattern similar to that of other legume starches. Under SEM they appeared smooth with no evidence of fissures. They showed a normal distribution of diameters with a range of 15.5–59.8 μ and a mean of 33.5 μ. Tepary starch had an amylose content of 30.7% and a gelatinization temperature range of 70.5–84.0°C. Other properties were also determined. Fractionation provided an amylose fraction with a β‐amyloysis limit of 76.3% and an average DPη of 618. The amylopectin fraction had an average magnified image values of 33, 22 and 10 glucose units respectively.

In vitro digestibility of starch from tepary bean, Phaseolus acutifolius var. latifolius. was determined in comparison with tepary bean flour and maize starch. The extent of sample hydrolysis by a-amylase was measured as mg reducing sugar (maltose) released per 100 mg substrate. After 2 h incubation at 37"C, values obtained for tepary starch. tepary flour and maize starch treated in various ways were as follows: raw 8.0.8.6 and 25.6; freeze dried 2.6,3.2 and 17.8; autoclaved 7.4,5.7 and 27.7; cooked (15 min) 81.7.23.1 and 87.8: resp. Raw tepary starch was more resistant to hydrolysis than maize starch due, perhaps, to differences in granule structure and amylose content. Freeze-drying and autoclaving slightly decreased digestibility of both tepary starch and flour. Cooking greatly increased susceptibility to hydrolysis for each substrate. The rate of increase was reduced after 15 min exposure to enzymes, and no appreciable difference was found between cooked tepary and maize starches. Teparybohnen-Stlrke. Teil 3: In vitro-Abbaubarkeit. Die Abbaubarkeit der Starke der Tepary-Bohne (Phaseolus acutifolius var. latifolius) wurde in iirro bestimmt und mit Teparybohnen-Mehl und Maisstarke verglichen. Der Hydrolysegrad der Proben durch a-Amylase wurde anhand der Freisetzung von reduzierendem Zucker (in mg Maltose) je 100 mg Substrat gemessen. Nach 2 h Inkubationszeit bei 37°C wurden folgende Werte fur Teparystarke. Teparymehl und Maisstarke gemessen: roh 8,0 8.6 und 25.6: gefriergetrocknet 2.6, 3.2 und 17.8; autoklaviert 7,4, 5,7 und 27,7: gekocht (15 min) 81,7, 23.1 und 8 7 8 . Rohe Teparystarke war gegenuber der Hydrolyse widerstandsfahiger als Maisstarke, offenbar aufgrund von Unterschieden in der Kornstruktur und im Amylosegehalt. Gefriertrocknung und Autoklavieren verminderten geringfiigig die Abbaubarkeit von Teparystarke und Teparymehl. Kochen erhohte die Hydrolyseempfindlichkeit allcr Substrate betrachtlich. Eine 15minutige Enzyminkubation verminderte dagegen die Steigerungsrate. Nennenswerte Unterschiede zwischen gekochter Tepary-und Maisstarke konnten nicht festgestellt werden.

Tepary samples were examined for patterns of hydration, dry matter losses during the processes of soaking and cooking, residual hardness in partially cooked samples and heat lability of endogenous proteinaceous antinutritional factors. At 24 °C, teparies imbibed water equivalent to their weight (100% hydration) in 4h and continued to absorb water rapidly for an additional 4 h before reaching an equilibrium hydration. During the processes of soaking and cooking, materials leached from raw beans represented 7.3 and 13.5 % of their dry weight, 4.3 and 12.4% of their protein content, 7.1 and 12.2% of their stored carbohydrate and 22.4 and 33.4% of their mineral levels, respectively. In samples prepared at different cooking times (60, 90, 120, 150, 180min) and cooking temperatures (80, 85, 90, 95 °C), longer times and higher temperatures resulted in greater reductions in residual bean hardness; interactive effects of time and temperature treatments were significant. Residual activity of trypsin and chymotrypsin inhibitors in partially-cooked samples appeared to be negligible. In addition, at least 80 % of the original hemaglutinating activity of lectins in raw beans was lost during partial-cooking of samples under all cooking regimes.

Rheological and organoleptic properties of starch from tepary bean (Phaseolus acutifolius var. latifolius) have been investigated. Gelatinization was determined to be a single‐step process. The pasting properties were similar to those reported for other legume starches. It was stable when cooked at 95°C for 15 min and showed a progressive increase in viscosity when cooled to 50°C. At 4 and 6% concentrations (w/w) tepary starch pastes exhibited a type C viscosity pattern whereas at concentrations of 7% and above, pasting behavior resembled a type B pattern. Effects of pH and the influence of sucrose, salt and oil on pasting behavior were also examined. Sensory evaluation of vanilla pudding prepared with tepary starch established its potential consumer acceptance.