Effect of mixing time, freeze-drying and baking on phenolics, anthocyanins and antioxidant capacity of raspberry juice during processing of muffins

BACKGROUND: Consumption of baked products constitutes an important part of a daily breakfast considering that people are continually grabbing meals on the go. Among baked products, muffins rank third in breakfast products and attract a broad range of consumers. Incorporation of red raspberry juice into muffins can add value to the product while preserving health benefits to the consumer. The purpose of this study was to evaluate the effect of mixing time, freeze‐drying and baking on the phenolic and anthocyanin contents and antioxidant capacity of raspberry juice during the preparation of muffins. RESULTS: Freeze‐drying of raspberry batters reduced their phenolic content and antioxidant capacity regardless of mixing time. Non‐freeze‐dried raspberry batter mixed for 5 min had the highest phenolic content (0.88 mg gallic acid equivalent g^?1 dry matter (DM)). Non‐freeze‐dried raspberry muffins had the highest antioxidant capacity (0.041 µmol Trolox equivalent g^?1 DM). Freeze‐dried raspberry batters mixed for 5 and 10 min had the highest anthocyanin content (0.065 mg cyanidin‐3‐glucoside g^?1 DM). Baking reduced the anthocyanin content of both non‐freeze‐dried and freeze‐dried raspberry muffins. CONCLUSION: Despite the reduction in valuable compounds, muffin is a vehicle for the delivery of these compounds. Copyright © 2012 Society of Chemical Industry     

Ripening temperature affects the content and distribution of isoflavones in sufu,a fermented soybean curd

Sufu, a fermented soybean curd, was prepared by ripening the salted tofu cubes in the Aspergillus oryzae‐fermented rice–soybean koji mash at 25, 35 or 45 °C for a period of 16 days. It showed that the 16‐day ripened sufu contains less total isoflavone content (629.29–739.68 μg g^?1 dried matter) than the salted tofu before ripening (942.59 μg g^?1 dried matter). Regardless of ripening temperature, ripening causes a major reduction in the content of β‐glucoside and malonylglucoside isoflavones along with a significant increase of aglycone isoflavone content. These changes were enhanced as the ripening period extended. Among the various treatments examined, sufu ripened at 45 °C showed the greatest increase in aglycone content coupled with the greatest decrease in malonylglucosides. The distribution of malonylglucosides decreased from an initial 40.32% in the tofu cube to 9.78% after 16 days of ripening at 45 °C. Meanwhile, the distribution of aglycone increased from 13.17% to 39.88%.     

Effect of pretreatments and drying temperatures on sweet potato flour

Effect of pretreatments with 1 w/v% sodium hydrogen sulphite (NaHSO₃) and 1 w/v% calcium chloride (CaCl₂) and drying temperatures (55, 60 and 65 °C) on sweet potato flour were investigated. Flour treated with CaCl₂ had higher amounts of ascorbic acid and β‐carotene (10.61–12.54 and 3.26–3.46 mg 100 g^?1 wet basis, respectively) than that treated with NaHSO₃ (9.47–11.47 and 3.05–3.43 mg 100 g^?1 wet basis, respectively). Total phenolic content and water absorption index (wet basis) were highest at 65 °C when treated with NaHSO₃ (10.44 mg 100 g^?1 and 2.49 g g^?1 respectively) and CaCl₂ (9.52 mg 100 g^?1 and 2.85 g g^?1 respectively). Swelling capacity (wet basis) was highest at 60 °C when treated with CaCl₂ (2.96 g g^?1) whereas when treated with NaHSO₃ (2.85 g g^?1) it was highest at 55 °C. Freeze‐dried samples treated with NaHSO₃ had higher lightness and total phenolic content while CaCl₂‐treated samples had higher β‐carotene and ascorbic acid. The results showed that good quality flour could be produced after soaking in CaCl₂ and dried at 65 °C.     

Preparation of Acid‐Resistant Microcapsules with Shell‐Matrix Structure to Enhance Stability of Streptococcus Thermophilus IFFI 6038

Microencapsulation is an effective technology used to protect probiotics against harsh conditions. Extrusion is a commonly used microencapsulation method utilized to prepare probiotics microcapsules that is regarded as economical and simple to operate. This research aims to prepare acid‐resistant probiotic microcapsules with high viability after freeze‐drying and optimized storage stability. Streptococcus thermophilus IFFI 6038 (IFFI 6038) cells were mixed with trehalose and alginate to fabricate microcapsules using extrusion. These capsules were subsequently coated with chitosan to obtain chitosan‐trehalose‐alginate microcapsules with shell‐matrix structure. Chitosan‐alginate microcapsules (without trehalose) were also prepared using the same method. The characteristics of the microcapsules were observed by measuring the freeze‐dried viability, acid resistance, and long‐term storage stability of the cells. The viable count of IFFI 6038 in the chitosan‐trehalose‐alginate microcapsules was 8.34 ± 0.30 log CFU g^?1 after freeze‐drying (lyophilization), which was nearly 1 log units g^?1 greater than the chitosan‐alginate microcapsules. The viability of IFFI 6038 in the chitosan‐trehalose‐alginate microcapsules was 6.45 ± 0.09 log CFU g^?1 after 120 min of treatment in simulated gastric juices, while the chitosan‐alginate microcapsules only measured 4.82 ± 0.22 log CFU g^?1. The results of the long‐term storage stability assay indicated that the viability of IFFI 6038 in chitosan‐trehalose‐alginate microcapsules was higher than in chitosan‐alginate microcapsules after storage at 25 °C. Trehalose played an important role in the stability of IFFI 6038 during storage. The novel shell‐matrix chitosan‐trehalose‐alginate microcapsules showed optimal stability and acid resistance, demonstrating their potential as a delivery vehicle to transport probiotics.     

Antioxidative and reducing capacity,macroelements content and sensorial properties of buckwheat‐enhanced gluten‐free bread

Common buckwheat flour (BF) was used to substitute 10%, 20%, 30% and 40% of corn starch, the main component of a gluten‐free bread formula, to make buckwheat‐enhanced gluten‐free breads. The 40% BF‐enhanced gluten‐free bread showed the highest antioxidant capacity against ABTS⁺˙ and DPPH˙ radicals (4.1 and 2.5 μmol Trolox g^?1 DM, respectively) and reducing capacity measured by cyclic voltammetry (1.5 μmol Trolox g^?1 DM). The antioxidant and reducing capacity of buckwheat‐enhanced gluten‐free breads were positively correlated with their total phenolic contents (r = 0.97). The 40% BF‐enhanced gluten‐free bread showed the highest overall sensory quality (7.1 units) when compared to control gluten‐free bread (1.8 units). The linear relationship between applied increasing BF doses in gluten‐free bread formula and magnesium, phosphorus and potassium content in breads was noted. It was concluded that 40% BF‐enhanced gluten‐free bread could be developed and dedicated to those people suffering from coeliac disease.     

Compositional variation in β‐carotene content,carbohydrate and antioxidant enzymes in selected banana cultivars

Banana is one of the most important tropical fruits, and India ranks first in its world production. Banana cultivars rich in provitamin A carotenoids may offer a potential food source for alleviating vitamin A deficiency, particularly in developing countries. With a view to exploit banana peels as a source of valuable components, in the present study, proximate composition, carotenoids, beta‐carotene and some anti‐oxidative enzymes as well as carbohydrate content of selected Indian banana varieties were determined. Karpooravalli cultivar of banana showed the maximum accumulation of carotenoid content in the non‐edible (68 μg g^?1 d.w.) portion of banana, while being the second highest in beta‐carotene content (143.12 μg per 100 g). However, Red Banana ranked highest in total carotenoid contents for pulp (4 μg g^?1 d.w.) and beta‐carotene was estimated to be the highest in the case of peels (241.91 μg per 100 g) and in pulp (117.2 μg per 100 g). Karpooravalli cultivar of banana is also rich in carbohydrate content in terms of total starch (1786.0 μg g^?1 d.w. in peels and 544.85 μg g^?1 d.w. in pulp) and sugars (53.53 μg g^?1 d.w. in peels and 39.05 μg g^?1 d.w. in pulp). The catalase enzyme activity in these peels ranged from 5.66 to 35.57 nmol min^?1 mg^?1 proteins and was found at a higher level in cultivar Poovan, while the ascorbate peroxidase showed the range of 2.25 to 6.22 μmol min^?1 mg^?1 proteins. The peels of cultivars Red Banana and Karpooravalli are rich source of bioactive compounds, such as carotenoids (beta‐carotene), anti‐oxidative enzymes and carbohydrate contents.     

Characterisation of pore properties of deep‐fat‐fried chicken nuggets breading coating using mercury intrusion porosimetry technique

The objective of this study was to characterise the pore properties of deep‐fat‐fried chicken nuggets coating under different processing conditions namely frying temperatures (170, 180 and 190 °C) and time (0–240 s) using porosimetry technique. Porosity range obtained was between 39.93 and 68.99%. Porosity of the freeze‐dried samples decreased with frying time. The main effect of temperature on porosity was significant (P < 0.05). Porosity showed a high positive and negative correlation with moisture and fat contents, and the correlation coefficients ranged between 0.88 and 0.96 and 0.78 and 0.8, respectively. Bulk density increased with frying time, while apparent density was relatively the same. Pore distribution showed bimodality. There was no significant effect of temperature on pore size distribution. Over 70% of the pore volume is made up of pores greater than 1 μm. Pore volume ranged between 0.54 and 1.5 cm³ g^?1, and it decreased with frying time. Mean pore diameter was between 0.006 and 389 μm, while with frying time, it ranged between 0.25 and 8.32 μm. Total pore area was between 2.53 and 16.53 m² g^?1. Hysteresis phenomenon showed that some of the pores were not perfectly cylindrical in shape.     

Studies on different combined microwave drying of carrot pieces

Three different combined microwave (MW) drying methods were compared, namely microwave‐assisted vacuum drying (MWVD), microwave‐assisted freeze drying (MWFD), microwave‐enhanced spouted bed drying (MWSD), in terms of drying rate, drying uniformity, product colour, rehydration ratio, retention of β‐carotene and vitamin C, and energy consumption. The drying rate of MWVD and MWSD were much faster than that of MWFD. The largest drying rate was obtained in MWSD with 3.5 W g^?1. In general, the colour of MWSD products was very uniform. Rehydration ratio of MWFD carrot pieces was almost the same as the freeze‐dried (FD) products and better than MWVD and MWSD products. In addition, the highest retention of carotene and vitamin C was observed in MWFD carrot pieces. No significant differences were observed in carotene and vitamin C between MWVD and MWSD products. However, the energy consumption in MWFD was the highest.     

Radical scavenging and anti‐proliferative capacity of three freeze‐dried tropical fruits

Tropical fruits are rich in antioxidant and anticancer phytochemicals, but their nutraceutical potential could be enhanced by drying technologies. Mango cv. Ataulfo, papaya cv. Maradol and pineapple cv. Esmeralda ripe pulps were freeze‐dried (?42 °C, 0.12 torr, 48 h) and their physicochemical and phytochemical profile, radical scavenging and antiproliferative capacity evaluated. The content of soluble solids, phenolic compounds and ascorbic acid was higher in mango (16.1^oBrix, 9.9 mg GAE per g and 9.6 mg g^?1) than in papaya/pineapple, but the later had more flavonoids (0.45 ± 0.05 mg QE per g). A fruit‐specific phenolic profile was detected by HPLC‐ESI‐QTOF‐MS, being shikimic (mango), chlorogenic (papaya), and protocatechuic (pineapple) acids the most abundant. Mango was the strongest radical scavenger and showed antiproliferative capacity (IC₅₀, μg mL^?1) in RAW 264.7 (100.7), HeLa (193.1) and L929 (138.5) cell lines. Papaya and pineapple extracts showed no antiproliferative activity. Freeze‐dried mango is a ready‐to‐eat functional food with better cancer preventing properties than papaya or pineapple.     

The influence of additives and drying methods on quality attributes of fish protein powder made from saithe (Pollachius virens)

BACKGROUND: Fish protein powder (FPP) is used in the food industry for developing formulated food products. This study investigates the feasibility of increasing the value of saithe (Pollachius virens) by producing a functional FPP. Quality attributes of spray and freeze‐dried saithe surimi containing lyoprotectants were studied. A freeze‐dried saithe surimi without lyoprotectants was also prepared as a control sample. RESULTS: The amount of protein, moisture, fat and carbohydrate in the FPPs were 745–928, 39–58, 21–32 and 10–151 g kg^?1. Quality attributes of FPPs were influenced by the two drying methods and lyoprotectants. The highest level of lipid oxidation was found in the control and the second highest in the spray‐dried FPP. The spray‐dried fish protein had the lowest viscosity among all FPPs. Gel‐forming ability of samples with lyoprotectants was higher than that of the control. Water‐binding capacity, emulsion properties and solubility of the freeze‐dried fish protein containing lyoprotectants were significantly higher than spray‐dried and control samples. However, functional properties of spray‐dried FPP were higher than the control sample. CONCLUSION: It is feasible to develop value‐added FPP from saithe surimi using spray‐ and freeze‐drying processes, but freeze‐dried FPP containing lyoprotectant had superior functional properties and stability compared with spray‐dried sample. Both products might be used as functional protein ingredients in various food systems. Copyright © 2010 Society of Chemical Industry     

Effect of drying conditions on bioactive compounds and antioxidant activity of broccoli (Brassica oleracea L.)

The effect of air‐drying parameters on antioxidant activity and changes in antioxidant compounds of broccoli (Brassica oleracea L.) were studied. Broccoli samples were dried to 70 g kg^?1 moisture content using temperatures ranging from 50 to 100 °C and air flow‐rates from 1.20 to 2.25 m s^?1, resulting in drying times from 25 to 90 min. Temperature, owing to its positive effect on the oxidation kinetics, was negatively correlated with ascorbic acid and free and total polyphenol contents but not with kaempferol, even though the sample dried at the highest temperature showed the lowest kaempferol content. The air flow‐rate was positively correlated with the total (TPP) and free (FPP) polyphenol contents because it led to a reduction in the drying time. No correlation was found between air flow‐rate and kaempferol content. Air flow‐rate and temperature positively affected the antioxidant activity by reducing the drying time. High‐temperature, short‐time processes maximised the antioxidant activity of broccoli owing to the negative effect of drying time on antioxidant activity. The antioxidant activity of broccoli was positively and significantly correlated with the FPP content but not with TPP and kaempferol. The evaluation of hydroxymethylfurfural content as an indicator of the occurrence of a Maillard reaction in dried broccoli did not support the hypothesis of a contribution of MRPs to the antioxidant activity of dried broccoli. Copyright © 2006 Society of Chemical Industry     

Changing soybean isoflavone composition and concentrations under two different storage conditions over three years

Soybean in Asia have been consumed in various forms, including soymilk, tofu and fermented products such as miso, temph and sufu. It is popularly regarded as a healthy food, partly owing to the isoflavones contained in their seeds. The objective of this study was to evaluate the variation of isoflavone concentration in soybean (Glycine max (L.) Merrill) seeds under different storage conditions for long storage periods. Isoflavone concentrations varied from 699.7 to 2581.6 μg g⁻¹ with cropping year, and acetylglucoside groups and glycitein were only detected in small amounts or traces in the eight soybean cultivars. The Daweon cultivar showed a variation between storage at room (−2039.0 μg g⁻¹) and low temperature (−1822.0 μg g⁻¹) over three years, while the isoflavone concentration in the Hannam cultivar only varied slightly (room temperature: −91.6 μg g⁻¹, low temperature: −81.2 μg g⁻¹). With storage at room temperature, the acetylglucoside group (+7.2 μg g⁻¹) slightly increased the isoflavone concentration, while the other three groups decreased it. In particular, the malonylglucoside group (−519.0 μg g⁻¹) showed a severe decrease. In the Myeongjunamul cultivar, genistin (+105.0 μg g⁻¹) resulted in the highest increase, while malonylgenistin (−958.7 μg g⁻¹) resulted in the greatest decrease in the Daweon cultivar. With storage at low temperature, other than malonylglucoside (−438.1 g g⁻¹), the other three groups, aglycon (+11.4 μg g⁻¹), glucoside (+45.2 μg g⁻¹) and acetylglucoside (+12.8 μg g⁻¹), increased the isoflavone concentration. Genistin (+136.0 μg g⁻¹) in the Muhan cultivar showed the highest increase, and malonylgenistin (−833.4 μg g⁻¹) in the Daweon cultivar showed the greatest decrease for storage under low temperature for three years. The variation of isoflavone concentration was positively correlated with the two different storage conditions (r² = 0.33), and total isoflavones were correlated with the concentration of the malonylglucoside (r² = 0.88***) and glucoside (r² = 0.80***) groups. Our study suggests that it may be feasible to improve the preservation method of soybean isoflavones as high functional substances for longer storage periods.     

Decreased fat accumulation in 3T3‐L1 pre‐adipocytes treated with extracts of heat‐processed soy flour and breads

The potential anti‐adipogenic effects of gluten‐free soy breads made from germinated soybean (GS), steamed soybean (SS) or roasted soybean (RS) were evaluated in an in vitro adipocyte cell model. GS and RS increased the total phenolic (TP) and total flavonoid (TF) contents of flours compared with the raw soybean (NS) flour. RS and GS had the highest TP (1.04 GAE mg g^?1) and TF (0.92 CAE mg g^?1) contents. Baking increased the TP content of breads, 0.09–0.26 GAE mg g^?1, compared with the flours. Fermentation during breadmaking increased the DPPH scavenging activities compared with the flours. The ABTS scavenging exhibited similar patterns to those of DPPH. Lipid accumulation in 3T3‐L1 cells shows that the alcoholic extracts (100 μg mL^?1) of SS flour and bread decreased adipocyte differentiation by 1.6‐ and 2.1‐fold, respectively, compared with control. SS bread extract substantially downregulated the adipogenesis‐related genes such as acetyl‐CoA carboxylase and glycerol‐3‐phosphate dehydrogenase.     

Isoflavone content of soybean cultivars grown in eastern Canada

Soybean (Glycine max (L) Merr) seeds contain isoflavones that have positive impacts on human health. The objective of this study was to determine isoflavone concentrations of early maturing soybean cultivars grown in different environments and to determine their relation to other important seed characteristics. Twenty soybean cultivars were grown in replicated trials at two sites in Montreal, Canada in 2002/2003 and their total and individual isoflavone concentrations were determined by high‐performance liquid chromatography. Seed yield, 100‐seed weight and oil, crude protein and crude fiber concentrations were concurrently determined. Total and individual isoflavone concentrations were significantly affected by cultivar, site and year. Total isoflavone concentration ranged from 360 to 2241 µg g^?1 and averaged 851 µg g^?1 across environments and cultivars. Variation across environments ranged from 20 to 100% for specific cultivars. Total isoflavone concentration was, on average, 40% greater in 2003 than 2002, which was characterized by above average temperatures and severe drought. Despite significant cultivar × year × site interactions, cultivars with consistently high and low isoflavone concentrations across environments were identified. Weak but significant positive correlations were observed between total isoflavone concentration and seed yield, 100‐seed weight and crude fiber, indicating that isoflavone concentration is positively associated with other desirable seed characteristics. Copyright © 2004 Society of Chemical Industry     

Chemical Composition, Antioxidant Capacity, and Sensory Quality of Pomegranate (Punica granatum L.) Arils and Rind as Affected by Drying Method

The objective of this study was to evaluate the application of: (1) freeze drying, (2) convective drying (50, 60, or 70 °C), (3) vacuum–microwave drying (240, 360, or 480 W), and (4) a combined method of convective pre-drying and vacuum–microwave finish drying in the processing of pomegranate arils and rind. The quality parameters under study included sugars and organic acids, punicalagins and ellagic acid, total polyphenols, total antioxidant activity, and sensory quality. In general, drying led to a reduction in all studied parameters; however, the behavior of arils and rind was different. Vacuum–microwave drying at 240 or 360 W was the best drying treatment for arils, while rind required freeze drying or soft conditions of convective drying (50 °C). Further research is needed to obtain proper results with convective pre-drying and vacuum–microwave finish drying of arils and rind. With proper selection of the drying protocol, high-quality dried arils will be available for consumers; these arils will be characterized by high contents of fructose (25 g 100 g^?1), phytic acid (2.2 g 100 g^?1), punicalagins (0.57 mg g^?1), total polyphenols (1.6 mg eq gallic acid g^?1), high antioxidant capacity (0.6 mg eq Trolox g^?1), and high intensities of garnet color, sweetness, sourness, and fresh pomegranate aroma. Besides, dried rind with very high contents of active compounds (123 mg g^?1 of punicalagins and 108 mg eq gallic acid g^?1) and high antioxidant capacity (26 mg eq Trolox g^?1) will be also available as functional material.     

Antioxidant activity and phenolic content of lentils (Lens culinaris), chickpeas (Cicer arietinum L.), peas (Pisum sativum L.) and soybeans (Glycine max), and their quantitative changes during processing

Total phenolic content (PC) was ～12 mg g^?1 in lentils, 2.2 mg g^?1 in chickpeas, 2.3 mg g^?1 in soybeans, 2.5 mg g^?1 in yellow peas and 1.2 mg g^?1 in green peas. Total antioxidant activity (AA) determined by ABTS (2,2′‐azinobis‐3‐ethyl‐benzthiazoline‐6‐sulfonic acid) assay was highest in lentils at around 14 μmol Trolox equivalent antioxidant capacity (TEAC) g^?1 and lowest in green peas at 1.9 μmol TEAC g^?1. Bound phytochemicals contributed to 82–85% total AA in lentils. Free phytochemicals contributed more to total AA in chickpeas, yellow peas, green peas and soybeans than bound phytochemicals. AA and PC was reduced by ～80% in lentils and <30% in yellow peas by decortication, by 16–41% in lentils, chickpeas and peas by cooking, and by 22–42% in lentils by soaking. Total AA was significantly correlated with total PC. Soybeans had the greatest ability to scavenge free radicals, inhibit lipid peroxidation and chelate metals among the legumes tested. Different legumes exhibited different AA mechanisms.     

Stability of anthocyanins in frozen and freeze-dried raspberries during long-term storage: in relation to glass transition

Abstract: Anthocyanins, natural plant pigments in the flavonoid group, are responsible for the red color and some of the nutraceutical benefits of raspberries. This study explores anthocyanin degradation in frozen and freeze‐dried raspberries during storage in relation to glass transition temperatures. Frozen raspberries were stored at ?80, ?35, and ?20 °C, while freeze‐dried raspberries were stored at selected water activity (a_w) values ranging from 0.05 to 0.75 at room temperature (23 °C) for more than a year. The characteristic glass transition temperatures (T′_g) of raspberries with high water content and glass transition temperature (T_g) of raspberries with small water content were determined using a differential scanning calorimeter. The pH differential method was used to determine the quantity of anthocyanins in frozen and freeze‐dried raspberries at selected time intervals. The total anthocyanins in raspberries fluctuated during 378 d of storage at ?20 and ?35, and ?80 °C. Anthocyanin degradation in freeze‐dried raspberries ranged from 27% to 32% and 78% to 89% at a_w values of 0.05 to 0.07 and 0.11 to 0.43, respectively, after 1 y. Anthocyanins were not detectable in freeze‐dried raspberries stored at a_w values of 0.53 to 0.75 after 270 d. First order and Weibull equations were used to fit the anthocyanin degradation in freeze‐dried raspberries. The 1^st‐order rate constant (k) of anthocyanin degradation ranged from 0.003 to 0.023 days^?1 at the selected water activities. Significant anthocyanin degradation occurred in both the glassy and rubbery states of freeze‐dried raspberries during long‐term storage. However, the rate of anthocyanin degradation in freeze‐dried raspberries stored in the glassy state was significantly smaller than the rate of anthocyanin degradation in the rubbery state.     

Improved Peanut Flour for a Reduced-Fat Peanut Butter Product

A commercial peanut flour (12% fat) was mixed with water (30% w/w), homogenized and drum‐dried in a double drum dryer. The drum clearance was adjusted to result in thin dried sheets which on milling resulted in a very fine, single banded particle size flour. The flour was no longer gritty and was used to dilute fat by mixing with full fat (52.5%) paste to obtain a 30% fat reduction in the peanut butter product. Response surface methodology, RSM, was used to optimize drum temperature (T), speed (S), and clearance (C) in order to minimize stickiness and hardness, maximizing oil separation and particle size. Based on surface responses and contour plots, optimum conditions were: T = 135 °C, S = 1 rpm and C = 0.33 mm. Optimum values predicted by RSM for peanut flour particle size, peanut butter stickiness, hardness, and oil separation were: 49.65 μm, 12347 N, 311.4 N and 6.87% respectively. Close agreement between experimental and predicted values was obtained.     

Comparison of the effect of microwave freeze drying and microwave vacuum drying upon the process and quality characteristics of potato/banana re‐structured chips

This study investigated the drying characteristics of microwave freeze‐drying (MFD)/microwave vacuum drying (MVD) of banana/potato restructured chips of varying proportion and microwave power. The results showed the MFD drying time had a maximum one‐hour time difference between the samples treated with 2 W g^?1 and 3 W g^?1 microwave power; and the higher potato content samples have about 30 min predominance than low potato content samples in drying time and the total drying time of MVD samples was less than 60 min. For the rehydration ratio, MFD samples were far superior to the MVD samples. The MFD samples had more than 4.5 rehydration ratio. The data of the colour difference metre showed that 3 W g^?1 microwave power would make samples slightly charred. The biggest differences between the MFD and MVD chips lie in their texture and shape; the hardness of MVD samples was 30.86 N, thrice higher than MFD samples.     

Influence of drying conditions on functional properties of potato flour

Gel consistency, pasting behaviour, sedimentation volume and swelling and solubility of potato flour, prepared by two different drying methods were determined. The functional properties of flour were changed markedly in drum drying due to severe molecular degradation whereby its digestibility was also increased compared to native and hot air dried flour. Amylose content of drum dried flour increased and its soluble amylose was doubled as a result of processing. Processing further effected agglomeration of starch granules with altered morphological features. B-type X-ray diffraction pattern was obtained for the native starch whereas V-type patterns were observed for the processed samples. Crystallinity index of drum dried flour was much lower and indicated the loss of granular surface and crystallinity. The reduction in peak intensities of starch of processed samples was observed in ¹³C NMR though the basic molecular structure remained unaffected. From these results an optimum amount of processed potato flour is expected to be used to achieve desirable properties for product development.