Effect of pretreatments on quality characteristics and water activity of air-dried litchis (Litchi chinensis Sonn.) cv. Rose Scented

The effect of pretreatments on the quality of dried litchis was studied. Dried whole litchis were brown, blanching in boiling water reduced browning but colour was still disliked. Peeling and destoning fruits before drying gave superior product (extent of browning or EB: 0.27, mean sensory score or MSS: 6.74) and they dried faster. Pre-drying dip of peeled and destoned litchis for 10 min in 2% Na₂SO₃ + 1% sodium metabisulphite at room temperature improved colour (EB 0.03) but reduced MSS (5.80). Litchis syruped in 40% syrup containing 0.5% citric acid and 3000 ppm SO₂ for 30 days gave best dried product (EB: 0.08, MSS: 8.08). They dried faster for first 4h after which untreated peeled and destoned (control) litchis dried faster. Dried syruped litchis were hygroscopic, water activity for product of 11.1% moisture (moisture free basis) was 0.27 and critical moisture content was 20g H₂O per 100g solids.     

Stability of fructooligosaccharides,sugars and colour of yacon (Smallanthus sonchifolius) roots during blanching and drying

Yacon (Smallanthus sonchifolius) root is an important source of fructooligosaccharides (FOS). This study evaluated the influence of the blanching and drying processes on the sugars, FOS and colour of the obtained flour. Blanching in boiling water of 5 mm slices for 6 min allowed to inactivate 95% of polyphenol oxidase and peroxidase activity. Blanching solutions containing ascorbic, citric and lactic acid were detrimental in terms of FOS retention (68.2–87.4%) due to hydrolysis mainly of GF3, GF4 and GF5 FOS, and also important losses of reducing sugars (RS) were observed (69.5–87.4% retention). Blanching treatments that included ascorbic acid/CaCl₂ prevented RS and FOS losses and improved colour of the obtained flour. The drying tested temperatures of 50–80 °C did not affect the RS retention and FOS losses associated to hydrolysis and the use of 80 °C rapidly reduced the water content and minimised browning reactions yielding flours with excellent colour characteristics with high FOS content that can be derived to the elaboration of prebiotic containing functional foods or for the extraction and purification of FOS.     

Effect of vacuum frying on main physicochemical and nutritional quality parameters of pineapple chips

BACKGROUND: Slices of MD‐2 pineapple hybrid were vacuum fried at 24 kPa according to a central composite experimental design that simultaneously varied frying time (6.3–7.7 min) and temperature (106.3–117.7 °C). Major physicochemical and nutritional quality factors were measured and modelled using a second‐order polynomial equation. RESULTS: Moisture content, water activity a_w, colour parameters L*, C* and H* and total vitamin C content decreased while total phenolic content and dehydroascorbic acid content increased with increasing frying time and temperature. Oil content, hardness and hydrophilic antioxidant capacity reached minimum values near the centre of the experimental field. By superimposing contour curves, it was determined that processing conditions of 6.9 min frying time and 112 °C frying temperature produced pineapple chips with a golden colour (L*≥ 60, C*≥ 50, H*≥ 80), an a_w of less than 0.29, a moisture content of about 4% and a hardness of less than 1.9 N, giving rise to a crispy texture. Oil content was about 20% (d.b) and residual total vitamin C content (～90 mg per 100 g wet basis (w.b.)) was high. Phenolic compound content was about 150 mg gallic acid equivalents per 100 g w.b. and antioxidant capacity was around 22 µmol Trolox equivalents g^?1 w.b. CONCLUSION: Vacuum frying is a dehydration process that produces healthy fruit snacks which partially preserve the fruit's original colour and nutritional compounds and have a high hydrophilic antioxidant capacity. Copyright © 2008 Society of Chemical Industry     

EFFECTS OF BLANCHING METHOD ON THE QUALITY CHARACTERISTICS OF FROZEN PEAS

This study evaluated the effects of microwave blanching prior to freezing as an alternative pretreatment for frozen peas. Peas were blanched (steam‐, boiling water immersion‐, microwave‐ or microwave‐blanched in a bag), frozen and evaluated after 0, 6 and 12 weeks for moisture and ascorbic acid content, peroxidase activity, visual appearance and instrumental color, and after 6 and 12 weeks for aroma, flavor and texture. All blanch treatments reduced peroxidase activity by 97% compared with controls (unblanched); blanching methods did not differ. Steam blanching resulted in significantly better ascorbic acid retention than all other treatments; microwave blanch treatments were either equivalent to or better than boiling water immersion. Both microwave treatments darkened (L* value) peas. Microwave‐blanched peas were visually greener than other treatments, but their appearance was less intact. Aroma and flavor were similar among blanch treatments. Texture of boiling water immersed peas was similar to the two microwave treatments.     

Pretreatments Effect in Drying Behaviour and Colour of Mature and Immature ‘Napolitana’ Sweet Cherries

The effect of different treatments on drying behaviour and colour of mature and immature cherries (Napolitana var.) has been studied. Drying was carried out at 70 °C with air at 4 m/s speed and 8 % relative humidity, and fruits were subjected to the following pretreatments: B (blanching), F (freezing), P (pitting), B?+?Dip1 (blanching and immersion in acid solution) and B?+?Dip1?+?Dip2 (blanching and immersion in saline acid solution) which affected the drying behaviour and the colour retention of fruits for both maturity degrees. Regarding skin colour in terms of chroma and hunter a parameters, the anthocyanin retention and the evaluation of anthocyanin degradation index, both B?+?dip1 and B?+?dip1?+?dip2 pretreatments led to better-quality dry products, mainly in mature cherries. Moreover, the incorporation of blanching in the combined pretreatments significantly reduced drying time. Lewis, Page and Logarithmic models were selected to represent in a simple way the thin-layer drying characteristics of pretreated cherries and to predict the process times required to reduce the moisture content to about 0.3–0.4 kg water/kg dm (a _w?≤?0.6). Logarithmic model provided the best fit to experimental data for each drying curve, based on the statistical tests used for evaluation.     

Effect of blanching and drying treatments on quality of bamboo shoot slices

The enzymes activity, texture, pectin, microstructure and colour change in bamboo shoots (Dendrocalamus latiflorus) were examined to evaluate the effect of blanching and drying treatments on quality of bamboo shoot slices (BSS). Peroxidase (POD), phenylalanine ammonia‐lyase and polyphenol oxidase in BSS will become completely inactive at 95 °C for 6‐, 9‐ and 12‐min blanching treatments, respectively. The hardness and protopectin (PP) content decreased after the blanching treatment. Meanwhile, the content of water‐soluble pectin increased initially and then decreased gradually during the blanching. After the blanching treatment, the L* and a* of BSS decreased, while b* increased, ΔE > 2. The hardness of rehydrated BSS decreased by 43.57% after freeze drying (FD), which, however, decreased more after hot air drying (HAD). The pectin of rehydrated BSS was also determined to explain the hardness change in BSS. The BSS acquired similar microstructure of fresh samples after FD, while microstructure of BSS was severely damaged after HAD. The colour of BSS changes significantly after drying treatment. However, FD can maintain better colour of BSS than HAD. The results may provide a reference for industrial production of BSS.     

Fluidized bed and tray drying of thinly sliced mango (Mangifera indica) pretreated with ascorbic and citric acid

The purpose of this work was to determine the influence of air temperature, sample diameter and antioxidants on water activity, moisture content and colour difference of thinly sliced mango in a fluidized bed and tray dryer. Mango samples were treated with antioxidants solutions (ascorbic and citric acid) before the drying process. Fluidized bed and tray drying of control and treated samples were carried out at two temperatures: 50 and 60 °C. A fractional factorial design 2^4?1 was used in both drying methods. The Newton semi‐theoretical model was found to represent thin‐layer drying kinetics of mango. For both drying types, moisture content of thinly sliced mango was well characterised (R² ≥ 0.975) by the model. The temperature increment increases the drying constant and decreases the equilibrium moisture content and water activity of the dehydrated samples. Colour closest to the original colour of fresh mango was obtained when 2 cm diameter mango pretreated with citric acid (1%) was dehydrated by fluidized bed at 60 °C. In addition, it was observed that the drying time at equilibrium by using fluidized bed was lower (60 min) than the tray dryer (120 min).     

Effects of low temperature blanching on texture,microstructure and rehydration capacity of carrots

The effect on quality of stepwise blanching (first 10 min at 65 °C, 50 min holding time, and 1 min at 95 °C) prior to drying of carrot slices was compared with conventional blanching (95 °C, 1 min). As quality parameters, rehydration capacity (effective diffusivity D_e, equilibrium moisture content W_e), texture (puncture test) and microstructure (SEM and Cryo‐SEM) were chosen. Non‐significant differences were found between the W_e of stepwise blanched samples and conventionally blanched ones, both values being similar to the moisture content of fresh carrots. D_e of conventional blanched carrots was higher than for stepwise blanched ones. Maximum force of stepwise blanched samples was higher than those of conventionally blanched ones and not significantly different from fresh carrots. Microstructural observations showed that stepwise blanching preserved cell to cell contacts better than conventional blanching; this fact was attributed to pectin‐methyl‐esterase activation at 65 °C, resulting in the differences in the maximum force between both treatments. Conventionally blanched samples tended to separate along their cell walls, forming voids among the phloem parenchyma cells. These voids would be filled with water during rehydration, thus showing the slightly higher W_e and the higher D_e for conventionally blanched carrots. Copyright © 2005 Society of Chemical Industry     

Partial dehydration of cherry tomato at different temperature, and nutritional quality of the products

This study concerns the partial dehydration of cherry tomatoes (Lycopersicon esculentum, var. Shiren) to obtain a product with 25% initial water content. Two kinds of dried tomatoes were obtained using a forced air oven at 40, 60 and 80 °C for different lengths of treatment. The first type was dehydrated after immersion of the fresh tomatoes in an aqueous solution of citric acid, sodium and calcium chloride (10:10:24 g/l); the second was obtained with no pre-treatment. The products were characterised by measuring their CIE L*a*b* colour parameters and levels of l-ascorbic acid, lycopene and β-carotene to evaluate thermal damage during processing under the different conditions. Moreover, water activity and the formation of 5-hydroxymethylfurfural were also determined as an index of sugar heat degradation. Treatment with a dipping solution protected both the nutritional and chemical qualities of the partially dried cherry tomatoes. Temperature was directly related to browning, ascorbic acid loss and HMF formation, while no clear influence could be found for carotenoid degradation.     

Evaluation of blanching requirements of green French bean (Phaseolus vulgaris L.) pods on basis of thermal resistance of its peroxidase

Green pods of French beans CV, pant Anupam were blended with distilled water, filtered and extract pH was adjusted to 5.25, 5.65, 5.85, 6.25 or 6.65 using 20 % citric acid or 1 N NaOH. Thermal inactivation times (TIT) of peroxidase were determined by TIT tube method. The corrected F₁₀₀ [min] and z [°C] at the above five pH values were 1.77 and 15.8, 1.43 and 14.1, 0.95 and 11.0, 0.29 and 8.7, and 0.17 and 8.1, respectively. The corresponding energy of activation values were 157, 177, 218, 286 and 307 KJ mole^?1. The actual blanching times in boiling media calculated from the above data were 4.0, 3.5, 2.5, 1.0 and 0.5 min, respectively, showing that blanching requirements of French beans decreased with increase in the pH of the blanching media.     

Improving textural quality in frozen jalapeño pepper by low temperature blanching in calcium chloride solution

The effects of low temperature blanching in calcium chloride solution of jalapeño peppers prior to freezing, on firmness retention, pH, methanol, colour and calcium ions of the product, were evaluated by response surface methodology. Texture, methanol content and pH were affected by all of the variables studied (P = 0.05). The optimum response was obtained at temperatures of 63.3–66 °C, calcium chloride concentrations of 0.17–0.21 m , immersion time of 11.6–14.4 min, with a holding time after blanching of 56.6–66.1 min. Microscopic evaluation of the thawed pepper showed that blanching in CaCl₂ solution provided a protective effect in maintaining cell wall integrity.     

Impact of Extrusion on Red Beetroot Colour Used as Pre-extrusion Colouring of Rice Flour

This work reports on the stability of red beetroot colour used as pre-extrusion colouring of extrudates. Initially, process parameters such as feed moisture content, screw speed and die temperature were optimised using red beetroot colour for pre-extrusion colouring. The colour was monitored in terms of L* and a* values, and also as the percent retention. The optimised conditions that gave maximum retention of colour were a moisture content of 16%, temperature of 160 °C and screw speed of 170 rpm. The effect of citric acid and sodium bicarbonate on colour stability of extrudates during processing, and that of light and packaging materials (polyethylene and metallised polyethylene) during storage at ambient conditions were also evaluated. Addition of 1% citric acid reduced the colour requirement by 37.5%. Metallised polyethylene showed better retention of colour as evident from the time required for 50% loss of colour. The study highlights on the use of red beetroot colour for safe and attractive red-coloured extrudates, and could create a commercial impact.     

The effect of shape,blanching methods and flour on characteristics of restructured sweetpotato stick

The blanching methods and controlling dry matter content used in the preparation of mashed sweetpotato (SP) for producing restructured sweetpotato stick (RSS) were studied. The two shapes of trimmed tuber were sliced and diced. Blanching was conducted by (i) boiling for 2 min in water at 100 °C and (ii) blanching in water at 100 °C containing 1% (w/v) sodium tripolyphosphate (STP) for 2 min. Controlling the dry matter content of dough was conducted by adding SP flour (0%, 5%, 10%, 15% and 20%). Chemical and physical characteristics were determined on the final product. The results from this study showed that blanching in 1% STP for 2 min improves colour and ash content of fried stick. Mixing of 5% SP flour with mashed SP produces suitable dough for further processing. RSS can be produced by a combination of blanching in 1% STP and mixing with 5% SP flour produce an intermediate hardness, high lightness and low redness colouration of RSS.     

Effectiveness of organic acid,ozonated water and chlorine dippings on microbial reduction and storage quality of fresh‐cut iceberg lettuce

BACKGROUND: The comparative effects of organic (citric and lactic) acids, ozone and chlorine on the microbiological population and quality parameters of fresh-cut lettuce during storage were evaluated. RESULTS: Dipping of lettuce in 100 mg L⁻¹ chlorine solution reduced the numbers of mesophilic and psychrotrophic bacteria and Enterobacteriaceae by 1.7, 2.0 and 1.6 log₁₀ colony-forming units (CFU) g⁻¹ respectively. Treatment of lettuce with citric (5 g L⁻¹) and lactic (5 mL L⁻¹) acid solutions and ozonated water (4 mg L⁻¹) reduced the populations of mesophilic and psychrotrophic bacteria by 1.7 and 1.5 log₁₀ CFU g⁻¹ respectively. Organic acid dippings resulted in lower mesophilic and psychrotrophic counts than ozonated water and chlorine dippings during 12 days of storage. Lactic acid dipping effectively reduced (by 2.2 log₁₀ CFU g⁻¹) and maintained low populations of Enterobacteriaceae on lettuce for the first 6 days of storage. No significant (P > 0.05) changes were observed in the texture and moisture content of lettuce samples dipped in chlorine, organic acids and ozonated water during storage. Colour, β-carotene and vitamin C values of fresh-cut iceberg lettuce did not change significantly (P > 0.05) until day 8. CONCLUSION: Lactic and citric acid and ozonated water dippings could be alternative treatments to chlorine dipping to prolong the shelf life of fresh-cut iceberg lettuce. Copyright © 2007 Society of Chemical Industry     

Chemical pretreatments and partial dehydration of ash gourd (Benincasa hispida) pieces for preservation of its quality attributes

Ash gourd (Benincasa hispida) is a commonly consumed vegetable in Asian subcontinent. Cut ash gourd pieces undergo severe decay within two days probably due to physical, biochemical and microbiological activities. Ash gourd pieces were chemically pretreated with sodium salt of ethylene diamine tetra acetic acid (sodium EDTA), calcium chloride (CaCl₂), citric acid and potassium metabisulphite (KMS) and dehydrated up to 30 percent moisture with an aim to extend its shelf life. Storage study of these samples was done with respect to texture, colour, bacterial content and water holding capacity. Shelf life was extended from two days to one month. Pretreatment using a combination of 1 mM EDTA, 2.5 percent KMS, 0.5 percent citric acid and 2.5 percent CaCl₂ and partial dehydration to 30 percent moisture found to be a good method in preservation of cut ash gourd pieces.     

Acrylamide reduction in potato chips by using commercial asparaginase in combination with conventional blanching

In this research acrylamide reduction in potato chips was investigated in relation to blanching and asparaginase immersion treatments before final frying. Potatoes slices (Verdi variety, diameter: 40 mm, thickness: 2.0 mm) were fried at 170 °C for 5 min (final moisture content of ∼2.0 g/100 g). Prior to frying, potato slices were treated in one of the following ways: (i) Rinsing in distilled water (control I); (ii) Rinsing in distilled water plus blanching in hot water at 85 °C for 3.5 min; (iii) Rinsing in distilled water plus immersion in an asparaginase solution (10000 ASNU/L) at 50 °C for 20 min; (iv) Rinsing in distilled water plus blanching in hot water at 85 °C for 3.5 min plus immersion in an asparaginase solution (10000 ASNU/L) at 50 °C for 20 min; (v) Rinsing in distilled water plus blanching in hot water at 85 °C for 3.5 min plus immersion in distilled water at 50 °C for 20 min (control II). Blanching in hot water (ii) was almost as effective as asparaginase potato immersion (iii) in order to diminish acrylamide formation in potato chips (acrylamide reduction was ∼17% of the initial acrylamide concentration). When potato slices were blanched before asparaginase immersion, the acrylamide content of the resultant potato chips was reduced considerably by almost 90%. We have demonstrated that blanching of potato slices plus asparaginase treatment is an effective combination for acrylamide mitigation during frying. It seems to be that blanching provokes changes in the microstructure of potato tissue leading to an easier and more effective diffusion of asparaginase.     

Storage stability of pineapple slices preserved by combined methods

Storage stability during 3 months was evaluated for pineapple slices preserved by combined methods (blanching for 1 min with saturated vapour, a_w reduction by osmotic concentration in sucrose syrup, pH reduction by addition of citric acid, and the addition of 1000 parts per million (ppm) of potassium sorbate and 150 ppm of sodium bisulphite). Pineapple slices were microbiologically sound and their moisture content, °Brix, pH and a_w remained almost constant during storage with mean values of 71.8%, 26.1, 3.65 and 0.978, respectively. Total sulphite and potassium sorbate concentrations of the pineapple slices were reduced during storage at 5 and 25 °C, being final concentrations 51% and 38% and 63% and 48% of the initial concentrations, respectively. Colour, texture and sensory evaluation revealed that there were no significant (P < 0.05) changes between samples stored at 5 or 25 °C. Good overall acceptability (initial mean score 7.21) of preserved pineapple slices even after 3 months storage at 25 °C (final mean score 7.02) was observed.     

Shelf-Life Extension of Fresh Ready-to-Bake Pizza by the Application of Modified Atmosphere Packaging

Combined effects of modified atmosphere packaging (MAP) and refrigeration (7±1 °C) were studied on shelf-life extension of ready-to-bake pizza. The gas atmospheres in the present study included four variables, namely viz. MAP1, air (control); MAP 2, 100% CO₂; MAP 3, 100% N₂; and MAP 4, 50%CO₂/50%N₂. The effect of MAP variables was observed for moisture content, water activity, pH, titratable acidity, free fatty acids, peroxide value, thiobarbituric acid, tyrosine content, lycopene content and L* a* b* values. The results indicated that MAP with 100% CO₂ significantly inhibited the lipid oxidation, reduced proteolysis and prevented total acidity (less decrease in pH). Also, the MAP (MAP 2) showed preservative effect on colour indices and shelf life higher than other treatments. Sensory analysis showed that the control samples had a limited shelf life of 5 days while a significant increase in shelf life of 15 days (300% increase) was achieved under modified atmospheres for unbaked pizza samples.     

Effect of some thermal and chemical pretreatments on smoked Oyster mushroom quality

The effect of different thermal and chemical pretreatments on quality and enzyme activities of smoked mushroom was investigated. Mushrooms were blanched (water and steam) and dipped in different concentrations of sulphites (SO₂), hydrogen peroxide (H₂O₂), ethylene‐di‐amine tetra‐acetic acid (EDTA) and citric acid for 10 min before smoking. Enzyme activities, colour characteristics, microbiological and sensory examinations were carried out every 2 weeks up to 8 weeks of storage in refrigerator at 4 °C. Results could be concluded that smoked mushroom pretreated with SO₂, H₂O₂ and steam blanching had the best colour values, the better score for all sensory characteristics and lower non‐enzymatic browning compared with other pretreatments. The most effective pretreatment against total aerobic bacteria and yeast & moulds were citric acid, EDTA and steam, and then smoking of mushroom can be attributed to the reduction of microbial counts. The most effective pretreatments on quality and safety of smoked mushrooms were H₂O₂ and steam. It can be concluded that thermal and chemical treatments, rather than smoking of mushroom, reduce enzyme activities and are suitable to preserve mushrooms.     

EFFECT OF BLANCHING AND SULFITE TREATMENT ON THE QUALITY OF FROZEN CAULIFLOWER

The influence of blanching time and post-blanching sulfite treatment on the sensory quality and texture of frozen cauliflower were assessed after storage at -18°C for up to one year. The treated cauliflower florets, sealed in polyethylene bags, were placed in waxed paperboard cartons and frozen in a contact plate freezer at -35°C. Samples blanched for 3 min and dipped in a solution containing 1000ppm of SO₂ for 5 min gave a significantly (p<0.05) superior product even when stored for one year. The residual SO₂ content of 50 ppm found in these stored samples disappeared after a 3 min cooking in boiling water. Cauliflower texture was influenced by blanching time but the textural differences of blanched samples diminished following freezing and storage. After a 3 min cooking, the texture of all thawed samples were comparable to that of fresh cauliflower cooked for 10–12 min.