Baked sweetpotato textures and sweetness: An investigation into relationships between physicochemical and cooked attributes.

Sweetpotato varieties vary greatly in perceived textures and sweetness. This study identified physicochemical factors that influence these attributes in cooked sweetpotatoes. Fifteen genotypes grown on three plots were baked and evaluated by a trained descriptive sensory analysis panel for sweetness and 13 texture attributes. Mechanical parameters were measured by texture profile analysis (TPA); and composition (starch, cell wall material, sugar contents), starch properties (thermal, granule type ratios, granule sizes), and amylase activities were characterized. TPA predicted fracturability and firmness well, whereas starch and sugar contents, B-type starch granule ratio, and amylase activities influenced prediction of mouthfeel textures. Sweetness perception was influenced by perceived particle size and sugar contents; and maltose generation during baking was highly correlated with raw sweetpotato starch content. These relationships between physicochemical sweetpotato properties and baked textures and sweetness could benefit breeders and processors in selecting biochemical traits that result in consumer preferred products.

Variable Effects of Twenty Sugars and Sugar Alcohols on the Retrogradation of Wheat Starch Gels.

Starch retrogradation is desirable for some food textures and nutritional traits but detrimental to sensory and storage qualities of other foods. The objective of this study was to determine the impact of sweetener structure and concentration on the retrogradation of wheat starch gels. The effects of 20 sweeteners selected based on common food usage and stereochemical structures of interest, and ranging in concentration from 10 to 50%w/w, on the retrogradation of wheat starch gels were monitored spectrophotometrically over time. The sweeteners were sucrose, xylose, ribose, glucose, galactose, fructose, mannose, mannitol, L-sorbose, xylitol, tagatose, allulose, maltose, lactose, isomaltulose, isomalt, sorbitol, maltitol, and raffinose. Retrogradation rates and amounts were compared by Avrami equation rate constants (k = 0.1-0.7) and absorbance values measured on day 28 (Abs = 0.1-1.0), respectively. Both sweetener concentration and type significantly affected retrogradation. Gels made with sugar alcohols and high sweetener concentrations (≈≥40%) tended to retrograde more and faster, whereas gels made with sugars and low sweetener concentrations tended to have lower retrogradation rates and amounts. Sweeteners with more equatorial and exocyclic hydroxyl groups (e.g., glucose and maltitol) and those with larger molar volumes (e.g., isomaltulose and raffinose) tended to increase the rate and amount of retrogradation, particularly at higher concentrations. The impact of sweeteners on retrogradation was a balance of factors that promoted retrogradation (intermolecular interactions and residual short-range molecular order) and inhibiting behaviors (interference at crystallization sites), which are influenced by sweetener concentration and structure. Understanding which sweeteners at which concentrations can be used to promote or inhibit retrogradation is useful for product formulation strategies.

Sweetpotato chip texture and fat content: Effects of enzymatic modification of cell wall polymers.

Impacts of cell wall polymers on sweetpotato chip texture and fat content were investigated through enzymatic modification. Covington sweetpotato slices were treated with cellulase, hemicellulase, pectinase, pectin methyl esterase, protease, the enzyme blend Viscozyme, or no enzymes (control) at 40-45°C for 0.5-2 h. Treated slices were blanched, dried, and fried in triplicate per experimental condition. Breaking forces of 20 chips per frying replicate were measured followed by chip fat, moisture, sugar, alcohol insoluble solids, glass transition temperature, and color analyses. Untreated slices from each batch (daily check) were fried and analyzed to account for starting material variability. Viscozyme and protease-treated chips had the greatest reduction in breaking force from untreated chips (-30.9% and -23.7%, respectively), while pectin methyl esterase-treated chips had the lowest reduction in breaking force (-9.0%). Chips treated with Viscozyme for 2 h were 6.7-6.3 percentiles lower in fat than the control. Principal component analysis elucidated that chip breaking force was associated with unfried slice puncture force, alcohol insoluble solids, and chip color, and chip fat content was inversely associated with maltose content and glass transition temperature. Breaking down multiple cell wall polysaccharides or structural proteins weakened chip textures, while strengthening the pectic fraction resulted in harder chips. Chip fat reduction also occurred when multiple cell wall polysaccharides were broken down. Therefore, cell wall polymers impact sweetpotato chip texture and fat contents, and their attributes should be considered when selecting cultivars and processes for sweetpotato chips. PRACTICAL APPLICATION: Sweetpotato chips are an increasingly popular snack, but there is little understanding how cell wall polymers impact chip textures and fat contents. Raw sweetpotato slices were enzymatically treated to selectively modify cell wall polymers before frying. Chip breaking forces were lowered by protease or Viscozyme (cell wall enzyme blend) treatments, while breaking forces were increased with pectin methyl esterase. In addition, chip fat contents were reduced by the Viscozyme treatment. Since cell wall modifications could impact chip texture and fat content, cell wall polymer attributes should be considered in selection and processing of sweetpotatoes for chip manufacturing.

Relationships between isolated sweetpotato starch properties and textural attributes of sweetpotato French fries.

Sweetpotato French fry (SPFF) textures have been associated with dry matter and starch contents, but these do not fully account for all textural differences. This study investigated the relationships between the physicochemical properties of sweetpotato starch and textural attributes of sweetpotato fries. Starches from 16 sweetpotato genotypes that varied in dry matter content were isolated and analyzed. The amylose content, pasting temperatures and viscosities, and textural properties of equilibrated starch gels were measured. Correlational analysis was performed with the respective SPFF mechanical and sensory texture attributes. Sweetpotato starch amylose content ranged from 17.3% to 21.1%, and the pasting and gel textural properties varied significantly between starches. Starch from orange-fleshed sweetpotatoes had lower pasting temperatures than starches from yellow/cream-fleshed genotypes, 72.2 ± 2.0 and 75.5 ± 1.1 °C, respectively. Notable inverse correlations were observed between the starch pasting temperature and perceived moistness (r = -0.63) and fibrousness (r = -0.70) of fries, whereas SPFF denseness was positively associated with starch pasting viscosity (r = 0.60) and nonstarch alcohol-insoluble solids content. Fry textures were likely affected by cooked starch properties, which should be considered when selecting varieties for sweetpotato fries. PRACTICAL APPLICATION: Without the aid of a batter, sweetpotato French fries (SPFFs) tend to be soft and limp-undesirable attributes in a fried food. The physiochemical properties of starch, the most abundant component in sweetpotato fries, were further explored in this study to better understand the properties of sweetpotato starch that influence SPFF textures. These findings can be used by sweetpotato processors and breeders for developing new sweetpotato varieties that are designed for production of fried products with desirable textures.

Effects of Sugars and Sugar Alcohols on the Gelatinization Temperatures of Wheat, Potato, and Corn Starches.

The gelatinization temperature (Tgel) of starch increases in the presence of sweeteners due to sweetener-starch intermolecular interactions in the amorphous regions of starch. Different starch botanical sources contain different starch architectures, which may alter sweetener-starch interactions and the effects of sweeteners on Tgels. To document these effects, the Tgels of wheat, potato, waxy corn, dent corn, and 50% and 70% high amylose corn starches were determined in the presence of eleven different sweeteners and varying sweetener concentrations. Tgels of 2:1 sweetener solution:starch slurries were measured using differential scanning calorimetry. The extent of Tgel elevation was affected by both starch and sweetener type. Tgels of wheat and dent corn starches increased the most, while Tgels of high amylose corn starches were the least affected. Fructose increased Tgels the least, and isomalt and isomaltulose increased Tgels the most. Overall, starch Tgels increased more with increasing sweetener concentration, molar volume, molecular weight, and number of equatorial and exocyclic hydroxyl groups. Starches containing more short amylopectin chains, fewer amylopectin chains that span through multiple clusters, higher number of building blocks per cluster, and shorter inter-block chain lengths exhibited the largest Tgel increases in sweetener solutions, attributed to less stable crystalline regions.

Relative humidity-temperature transition boundaries for anhydrous ß-caffeine and caffeine hydrate crystalline forms.

Caffeine is a hydrate-forming polymorphic crystalline compound that can exist in α, ß, and hydrate forms. Phase transitions between hydrate and anhydrous forms of a crystalline ingredient, and related water migration, can create product quality challenges. The objective of this study was to determine the relative humidity (RH)-temperature phase boundary between anhydrous ß-caffeine and caffeine hydrate. The ß-caffeine→caffeine hydrate and caffeine hydrate→ß-caffeine RH-temperature transition boundaries were determined from 20 to 45 °C using a combination of water activity (aw ) controlled solution and vapor-mediated equilibration, moisture sorption, powder X-ray diffraction, and Fourier-transform infrared spectroscopy techniques. Two transition boundaries were measured: the ß-caffeine→caffeine hydrate transition boundary (0.835 ± 0.027 aw at 25 °C) was higher than the caffeine hydrate→ß-caffeine transition boundary (0.625 ± 0.003 aw at 25 °C). Moisture sorption rates for ß-caffeine, even at high RHs (>84% RH), were slow. However, caffeine hydrate rapidly dehydrated at low RHs (<30% RH) into a metastable transitional anhydrous state with a similar X-ray diffraction pattern to metastable α-caffeine. Exposing this dehydrated hydrate to higher RHs (>65% RH) at lower temperatures (20 to 30 °C) resulted in full restoration to a 4/5 caffeine hydrate. This transitional anhydrous state was unstable and converted to a less hygroscopic state after annealing at 50 °C and 0% RH for 1 day. It was postulated that the caffeine hydrate→ß-caffeine was the true ß-caffeine↔caffeine hydrate phase boundary and that ß-caffeine could be metastable above the caffeine hydrate→ß-caffeine transition boundary. These caffeine RH-temperature transition boundaries could be used for selecting formulation and storage conditions to maintain the desired caffeine crystalline form. PRACTICAL APPLICATION: Caffeine can exist as either an anhydrous (without water) or hydrate (internalized water) crystalline state. The stability of each caffeine crystalline form is dictated by humidity (or water activity) and temperature, and these environmental stability boundaries for the caffeine crystalline forms are reported in this manuscript. Conversions between the two crystalline states can lead to deleterious effects; for example, the presence of caffeine hydrate crystals in a low water activity food (e.g., powder) could lead to the relocation of the water in caffeine to other ingredients in the food system, leading to unwanted water-solid interactions that could cause clumping and/or degradation.

RH-temperature stability diagram of α- and ß-anhydrous and monohydrate lactose crystalline forms.

Lactose crystals exhibit polymorphic, deliquescent, and hydrate-forming traits and can exist in monohydrate, ß-anhydrate, stable α-anhydrate, and hygroscopic α-anhydrate (isomorphic desolvate) forms. The objective of this study was to identify the relative humidity (RH) and temperature boundaries at which anhydrate-hydrate transitions and deliquescence occur for these lactose crystal forms. The deliquescence point (RH0) of lactose monohydrate was determined by measuring the water activity (aw) of a saturated solution, and the RH0s of the anhydrates were determined using dynamic vapor sorption measurement techniques. Increasing temperatures from 20 to 50 °C resulted in decreases in RH0 from 99 to 98% RH for the monohydrate, 89 to 82% RH for the ß-anhydrate, and 87 to 82% RH for the stable α-anhydrate. The effects of temperature on the anhydrate-hydrate RH boundaries were determined using a combination of controlled aw equilibration, powder X-ray diffraction, and Fourier-transform infrared spectroscopy techniques. Increasing temperature from 20 to 50 °C resulted in increasing RHs of the anhydrate-to-hydrate boundaries: the ß-anhydrate-to-monohydrate boundary increased from 77 to 79% RH, the stable α-anhydrate-to-monohydrate from 63 to 79% RH, and the unstable α-anhydrate-to-monohydrate from 10 to 13% RH. This is the first report of an RH-temperature stability map for lactose crystalline forms.