Modeling Starch Digestograms: Computational Characteristics of Kinetic Models for in vitro Starch Digestion in Food Research.

Starch digestion is mostly investigated with in vitro techniques, and time-course measurements are common. These yield digestograms that are modeled by theoretical, semitheoretical, and empirical kinetic equations, many of which are reviewed here. The Duggleby model has Michaelis-Menten functions, and its dependent variable is on both sides of the equation with no apparent parameter for maximum digestible starch (D∞ ). The Gaouar and Peleg models are equivalent. They predict both the initial digestible starch (D0 ) and D∞ , and an average digestion rate, but they can reveal "biratial" digestions. The first-order kinetic model exhibits diverse predictabilities and, when linearized, D∞ is sometimes equated to 100 g/100 g dry starch (100%), it yields an average rate of digestion and can predict negative D0 . The log of slope (LOS) model is unique in revealing the rapid-to-slow digestion rate phenomenon, but without guidelines to identify such. The LOS model does not sometimes use all the digestogram data, can predict D∞ greater than 100%, and returns zero digestion rate for some digestograms. However, some starchy materials exhibit a slow-to-rapid digestion rate phenomenon, as demonstrated with an example. The modified first-order kinetic model uses all the digestogram data with practical constraints (D0  ≥ 0 g/100 g dry starch; D∞  ≤ 100 g/100 g dry starch), describes all digestograms, and yields an average digestion rate, but it can also be used for "biratial" digestions. In addition, the logistic and Weibull models are discussed. Using some published data, the computational characteristics of these commonly used models are presented with objective parameters to guide choices.

Carotenoid contents of extruded and non-extruded sweetpotato flours from Papua New Guinea and Australia.

Carotenoid contents of extruded and non-extruded flours of Papua New Guinean and Australian sweetpotato cultivars were studied, using spectrophotometry and high performance liquid chromatography (HPLC). The cultivars differed (p<0.05) in their total carotenoid and ß-carotene contents, and the Original Beauregard cultivar had the highest total carotenoid and ß-carotene contents among the cultivars. The spectrophotometry (84-1720 µg/g solids) method generally over-estimated the total carotenoid content compared to the more specific HPLC (23-355 µg/g solids) method. Extrusion significantly (p<0.05) decreased the ΔL(*) Hunter colour values, while the Δa(*), Δb(*), total colour change (ΔE), chroma (CR), and browning indices (BI) increased. With the extruder and screw configuration used, extrusion at 40% moisture and 300 rpm screw speed retained carotenoid maximally at more than 80%. This study reports, for the first time, carotenoids of flours from south Pacific sweetpotato cultivars, and carotenoid retention during extrusion.

Conservation of coconut (Cocos nucifera L.) germplasm at sub-zero temperature.

Protocols are proposed for the low (-20 degree C) and ultra-low (-80 degree C) temperature storage of coconut (Cocos nucifera L.) embryos. A tissue dehydration step prior to storage, and a rapid warming step upon recovery optimized the protocol. The thermal properties of water located within embryos were monitored using differential scanning calorimetry (DSC). In the most efficient version of the protocol, embryos were dehydrated under a sterile air flow in a dehydration solution containing glucose (3.33 M) and glycerol (15 percent) for 16 hours. This protocol decreased the embryo water content from 77 to 29 percent FW and at the same time reduced the amount of freezable water down to 0.03 percent. The dehydrated embryos could be stored for up to 3 weeks at -20 degree C (12 percent producing normal plants upon recovery) or 26 weeks at -80 degree C (28 percent producing normal plants upon recovery). These results indicate that it is possible to store coconut germplasm on a medium term basis using an ultra-deep freezer unit. However for more efficient, long term storage, cryopreservation remains the preferred option.

Kinetics of starch digestion in sweetpotato flours from Papua New Guinean and Australian cultivars.

Twenty-five sweetpotato cultivars from Papua New Guinea (PNG) and Australia were studied for their flour digestibility properties. The cultivars displayed monophasic digestograms, and a modified first-order kinetic model adequately predicted the rate and extent of starch digestion. Flours from all the cultivars had high average glycemic index (GIavg) and glycemic load (GL). This study of starch digestion in a wide range of sweetpotato cultivars demonstrates associations and interactions of non-starch components in the flours, and their effects on starch digestibility. The presence of resistant starch (RS) in some cultivars is highlighted with respect to its potential contribution to human health and nutrition.

Characterisation of grain quality in diverse sorghum germplasm using a Rapid Visco-Analyzer and near infrared reflectance spectroscopy.

BACKGROUND: Twenty-two diverse sorghum landraces, classified as normal and opaque types obtained from Ethiopia, were characterised for grain quality parameters using near infra-red spectroscopy (NIRS), chemical and Rapid Visco-Analyzer (RVA) characteristics. RESULTS: Protein content ranged from 77 to 182 g kg(-1), and starch content from 514 to 745 g kg(-1). The NIRS analysis indicated the pig faecal digestible energy range from 14.6 to 15.7 MJ kg(-1) as fed, and the ileal digestible energy range from 11.3 to 13.9 MJ kg(-1) as fed. The normal sorghums had higher digestible energy than the opaque sorghums, which exhibited lower RVA viscosities, and higher pasting temperatures and setback ratios. The RVA parameters were positively correlated with the starch content and negatively correlated with the protein content. The normal and opaque types formed two distinct groups based on principal component and cluster analyses. CONCLUSION: The landraces were different for the various grain quality parameters with some landraces displaying unique RVA and NIRS profiles. This study will guide utilisation of the sorghum landraces in plant improvement programs, and provides a basis for further studies into how starch and other constituents behave in and affect the properties of these landraces.

Ethnobotany, diverse food uses, claimed health benefits and implications on conservation of barley landraces in North Eastern Ethiopia highlands.

BACKGROUND: Barley is the number one food crop in the highland parts of North Eastern Ethiopia produced by subsistence farmers grown as landraces. Information on the ethnobotany, food utilization and maintenance of barley landraces is valuable to design and plan germplasm conservation strategies as well as to improve food utilization of barley. METHODS: A study, involving field visits and household interviews, was conducted in three administrative zones. Eleven districts from the three zones, five kebeles in each district and five households from each kebele were visited to gather information on the ethnobotany, the utilization of barley and how barley end-uses influence the maintenance of landrace diversity. RESULTS: According to farmers, barley is the "king of crops" and it is put for diverse uses with more than 20 types of barley dishes and beverages reportedly prepared in the study area. The products are prepared from either boiled/roasted whole grain, raw- and roasted-milled grain, or cracked grain as main, side, ceremonial, and recuperating dishes. The various barley traditional foods have perceived qualities and health benefits by the farmers. Fifteen diverse barley landraces were reported by farmers, and the ethnobotany of the landraces reflects key quantitative and qualitative traits. Some landraces that are preferred for their culinary qualities are being marginalized due to moisture shortage and soil degradation. CONCLUSIONS: Farmers' preference of different landraces for various end-use qualities is one of the important factors that affect the decision process of landraces maintenance, which in turn affect genetic diversity. Further studies on improving maintenance of landraces, developing suitable varieties and improving the food utilization of barley including processing techniques could contribute to food security of the area.

Characterisation of sweetpotato from Papua New Guinea and Australia: Physicochemical, pasting and gelatinisation properties.

The physicochemical and functional properties of flours from 25 Papua New Guinean and Australian sweetpotato cultivars were evaluated. The cultivars (white-, orange-, cream-, and purple-fleshed, and with dry matter, from 15 to 28g/100g), were obovate, oblong, elliptic, curved, irregular in shape, and essentially thin-cortexed (1-2mm). Flour yield was less than 90g/100g solids, while starch, protein, amylose, water absorption and solubility indices, as well as total sugars, varied significantly (p<0.05). Potassium, sodium, calcium, and phosphorus were the major minerals measured, and there were differences in the pasting properties, which showed four classes of shear-thinning and shear-thickening behaviours. Differential scanning calorimetry showed single-stage gelatinisation behaviour, with cultivar-dependent temperatures (61-84°C) and enthalpies (12-27J/g dry starch). Oval-, round- and angular-shaped granules were observed with a scanning electron microscope, while X-ray diffraction revealed an A-type diffraction pattern in the cultivars, with about 30% crystallinity. This study shows a wide range of sweetpotato properties, reported for the first time.

Dehydration improves cryopreservation of coconut (Cocos nucifera L.).

Cryopreservation of coconut can be used as a strategy to back up the establishment of living collections which are expensive to maintain and are under constant threat from biotic and abiotic factors. Unfortunately, cryopreservation protocols still need to be developed that are capable of producing a sizeable number of field-grown plants. Therefore, we report on the development of an improved cryopreservation protocol which can be used on a wide range of coconut cultivars. The cryopreservation of zygotic embryos and their recovery to soil-growing plants was achieved through the application of four optimised steps viz.: (i) rapid dehydration; (ii) rapid cooling; (iii) rapid warming and recovery in vitro and (iv) acclimatization and soil-supported growth. The thermal properties of water within the embryos were monitored using differential scanning calorimetry (DSC) in order to ensure that the freezable component was kept to a minimum. The feasibility of the protocol was assessed using the Malayan Yellow Dwarf (MYD) cultivar in Australia and then tested on a range of cultivars which were freshly harvested and studied in Indonesia. The most efficient protocol was one based on an 8-h rapid dehydration step followed by rapid cooling step. Best recovery percentages were obtained when a rapid warming step and an optimised in vitro culture step were used. Following this protocol, 20% (when cryopreserved 12 days after harvesting) and 40% (when cryopreserved at the time of harvest) of all MYD embryos cryopreserved could be returned to normal seedlings growing in soil. DSC showed that this protocol induced a drop in embryo fresh weight to 19% and significantly reduced the amount of water remaining that could produce ice crystals (0.1%). Of the 20 cultivars tested, 16 were found to produce between 10% and 40% normal seedlings while four cultivars generated between 0% and 10% normal seedlings after cryopreservation. This new protocol is applicable to a wide range of coconut cultivars and is useful for the routine cryopreservation of coconut genetic resources.