Optimization of stepwise blanching of frozen-thawed potato tissues (cv. Monalisa)

 Response surface methodology was used to compare the effect of temperature and time of the first step of blanching on compression, shear, tension and stress-relaxation parameters of frozen-thawed potato tissues. A central, composite rotatable design was used to study the effects of variation in levels of temperature (52.93–67.07  °C) and time (15.86–44.14 min) on rheological parameters. Blanching temperature was the most important factor affecting the mechanical properties tested. The models fitted for the apparent modulus of elasticity in compression, maximum tension force, and relaxed force in the first cycle (F _r1); all had R ²>0.85 (P≤0.01) and were used for doing predictions. Optimum conditions were with in the ranges of temperature (60–65  °C) and time (25–35 min) used for each factor. In the experimental verification of the models at 65  °C during 30 min, the lowest percentage residual between experimental and predicted values was obtained for F _r1 (0.644), which was therefore the most appropiate parameter for detecting the firming effect that the pectinesterase activity produced on frozen potato tissues as a consequence of stepwise blanching under these conditions. Received: 3 February 1999 / Revised version: 12 April 1999     

Improvement of oleuropein extractability by optimising steam blanching process as pre-treatment of olive leaf extraction via response surface methodology

Impact of steam, hot water blanching and UV-C irradiation as pre-treatments on extraction of oleuropein and related biophenols from olive leaves (OLs), was investigated. Moreover, particle size effect of olive leaves and steam blanching duration were selected as independent variables to optimise steam blanching process in terms of oleuropein content (OC) and antioxidant activity (AC) of ethanolic extracts, by using response surface methodology. Optimum conditions for OC and AC were 10 min steam blanching of 20–11 and 3–1 mm olive leaf fraction, respectively. Depending on the extraction procedure, at optimum conditions of steaming the results indicate that steam blanching of OL prior to extraction can significantly increase oleuropein yield from 25 to 35 times compared to non-steam blanched sample, whereas the antioxidant activity increased from 4 to 13 times. No significant UV-C effect was observed in OC and AC, while hot water blanched samples showed significantly higher oleuropein yields and antioxidant activity compared to untreated samples.     

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.     

Effect of natural extracts on the formation of acrylamide in fried potatoes

The objective of the present work was to evaluate the effect of natural extracts on the formation of acrylamide in fried potatoes. The aqueous extracts used were obtained from wild oregano (Origanum vulgare), thyme (Thymus vulgaris), cinnamon (Cinnamomum verum), bougainvillea (Bougainvillea spp) and green tea (Camellia sinensis), which presented a high percentage of free radical inhibition (DPPH) (48–99%) and content of total phenolic compounds (205–547 μg EAG/μg of d.w.). Potatoes were submerged in the antioxidant extracts at a concentration of 1 g/L for 1 min, before being fried and their acrylamide concentration quantified by GC–MS. The extracts from green tea, cinnamon and oregano reduced the acrylamide level by 62%, 39% and 17%, respectively. The potatoes submerged in cinnamon and bougainvillea extracts showed differences in the color parameters compared to the control potatoes (P < 0.05); however, no significant differences (P > 0.05) were found in the texture and the peroxide values. The sensorial evaluation showed that the acceptance of the potatoes was not affected by the treatment applied. Thus, we can conclude that pre-treating potatoes with antioxidants before frying produces beneficial effects such as a reduction in acrylamide content, without any significant changes in their physicochemical, sensorial and textural properties.     

Effect of formulation and processing parameters on acrylamide formation: A case study on extrusion of blends of potato flour and semolina

Acrylamide formation in extruded snacks prepared using blends of potato flour:semolina in ratios ranging from 30:70 to 70:30 showed maximum acrylamide formation in the 70:30 blend. The extrusion was carried out at a screw speed of 120 rpm, temperature of 170 °C and moisture content of 18%. Further, the influence of extrusion processing parameters on the acrylamide formation in extruded snacks prepared from a 70:30 blend of potato flour:semolina was investigated using response surface methodology (RSM). The feed moisture was varied from 12.6% to 19.4%, die temperature from 163 to 197 °C and screw speed from 106 to 173 rpm. The extrudates so obtained showed acrylamide content ranging from 704 to 1560 μg/kg. The effect of different additives such as citric acid, calcium salts, amino acids, vitamins and their combinations on the mitigation of acrylamide formation showed calcium chloride at 50 μmol/g flour blend to reduce acrylamide formation by 65% without altering the sensory properties of the extrudates.     

A methodology for evaluating the formation and human exposure to acrylamide through fried potato crisps

Potato crisps are a popular snack food which have been implicated as a potential source of acrylamide. This study develops a farm-to-fork human exposure assessment model for acrylamide in fried potato crisps for Irish consumers. The model used Monte Carlo simulation techniques to model the various stages from on farm production of potatoes, storage, processing, crisp production and final human consumption of potato crisps. A baseline model is created and a number of scenarios are subsequently created to look at the impact of different model assumptions and input parameters. The baseline model found that the mean level of acrylamide in potato crisps in Ireland was 720 μg/kg. Irish consumer exposure to acrylamide in potato crisps was estimated to be 0.052 and 0.064 μg/kg bw/day for males and females, respectively. A sensitivity analysis revealed the important parameters influencing the model predictions. The initial level of reducing sugars was found to be the most important parameter (correlation coefficient 0.58 and 0.57 for glucose and fructose, respectively), highlighting the importance of selecting cultivars with low reducing sugar levels for crisp production. The cooking regime had a significant impact on model predictions, highlighting the need for further research into the impact of different time and temperature combinations. Blanching and soaking of potatoes were also identified as important risk reduction processes.     

Impact of selected additives on acrylamide formation in asparagine/sugar Maillard model systems

The main purpose of this paper was to study the effect of selected additives, NaCl, NaHSO₃, ascorbic acid, cysteine and allicin, on acrylamide (AA) formation in asparagine/fructose (Asn/Fru) and asparagine/glucose (Asn/Glc) by microwave processing. Our results showed that NaHSO₃ and cysteine had the best reduction rate on AA formation, but the browning would be influenced by the addition of these additives. Ascorbic acid is another good inhibitor for AA formation both in Asn/Fru and Asn/Glc model systems, but the browning would be inhibited by the high concentration of ascorbic acid. Natural antioxidants are attractive candidates for the development of effective inhibitors for AA formation. In the present study, allicin effectively reduced AA formation and achieved a maximum reduction rate of > 50% for the use of allicin at a concentration of 0.0375% in Asn/Fru model system. While in Asn/Glc model system, allicin did not show good reduction rate. Through RSM study, the lowest AA content was 0.181 ??g/mL by the addition of allicin in Asn/Fru and 0.029 ??g/mL by the addition of ascorbic acid in Asn/Glc model system, respectively. The study could be regarded as a pioneer contribution on AA reduction in Maillard model system by the addition of allicin.     

Studies on the effects of blanching time, evaporation time, temperature and hydrocolloid on physical properties of chili (Capsicum annum var kulai) puree

Thermal processing of chili (Capsicum annum var Kulai) and canning in the form of puree is an alternate process of producing a product with extended shelf-life while retaining its favorable qualities. Red chili was subjected to blanching treatment at different temperatures and times in a steam-jacketed kettle. Test samples were removed, cooled, drained and tested for enzyme activity (peroxidase and lipoxygenase). The model of response surface methodology was introduced to investigate the effects of time, temperature and amount of pectin on the physical properties of chili puree subjected to the evaporation process. Pectin was used as a thickening agent to enhance the viscosity of the puree. A complete inactivation of the enzymes was obtained with the blanching temperature of 100 °C for 6 min. First-order reaction kinetics fitted adequately to predict color loss and pectin was found to improve the viscosity and total soluble solids of the puree.     

Potential for acrylamide formation in potatoes: data from the 2003 harvest

Reducing sugars, free amino acids, and the potential for acrylamide formation were determined in more than 50 potato samples from the 2003 harvest in Switzerland. The reducing sugar content strongly correlated with acrylamide, whereas no correlation was found between acrylamide and free asparagine or the pool of free amino acids. The reducing sugar contents and the acrylamide potentials were higher in most of the cultivars tested than in the samples from 2002. This was probably due to the hot and dry summer of 2003. Monitoring sugars and amino acids during heating at 120 °C and 180 °C showed that glucose and fructose reacted much faster than sucrose and the amino acids. Glutamine was consumed to a larger extent than any of the other amino acids. During prolonged storage, the reducing sugars decreased considerably while only moderate changes in the free amino acids were observed. Altogether, glucose and fructose remain the critical factors for acrylamide formation in potatoes and represent the most feasible way of reducing the formation of acrylamide in potato products.     

热烫预处理降低鲜切油炸薯片中丙烯酰胺的工艺优化研究

研究热烫预处理对鲜切油炸薯片中丙烯酰胺的影响和薯片油炸工艺优化。在相同条件下,分别对原料进行热烫和非热烫处理,在不同油炸温度和时间条件下进行油炸试验,采用DNS法测还原糖,液质联用法检测薯片中丙烯酰胺含量。结果表明,通过对切片的马铃薯进行热烫处理,即75℃热烫150s,能明显降低还原糖含量,160℃油炸120s,可降低丙烯酰胺含量至67.18μg/kg。     

The influence of variety, agronomical factors and storage on the potential for acrylamide formation in potatoes grown in Norway

Freeze-dried potato samples were obtained from the varieties Saturna and Peik that had been subjected to different agronomic conditions and storage. Powdered samples originating from the same growth year were mixed with oil and heated simultaneously in a stone oven in order to study the potential for acrylamide (AA) formation in a fixed time and temperature situation. For baked samples originating from unstored potato a linear relationship was found between asparagine (Asn) and reducing sugar (RS) content and AA formation. For these samples the AA content varied linearly with a* except from samples that originally were high or low in Asn. Upon storage the correlation between the quantity of the common precursors, Asn and RS, and AA were smaller. Results of the baking experiments suggest that the AA potential for stored potato cannot be predicted from RSs and Asn alone, and that other factors that might change during storage are of importance. Due to north European conditions the RSs might not always be the limiting substrate for AA formation. Additional information for the precursor content in 2004 and 2005 are included. No systematic effect on precursor contents related to chemical vine killing was observed. Precursor contents varied among and between varieties, different cultivation years and growth sites.     

Predicting the end point of a blanching process

Thermal inactivation of peroxidase and lipoxygenase during blanching of a solid food with a finite cylinder shape (diameter=9 cm and heitght=20 cm) has been mathematically studied in order to evaluate the end point of the process. Predictions included thermal inactivation of peroxidase and lipoxygenase during heating in steam of a conventional blanching process, and thermal inactivation of lipoxygenase during an individual and quick blanching process. It was assumed an inactivation biphasic model to describe the inactivation first-order thermal kinetics of peroxidase and lipoxygenase. Heat transfer conditions, the total initial indicator enzyme activity, the proportion of resistant and labile isoenzymes, kinetic parameters and the end point that the analytical method to be used may detect are important factors to predict and optimize a blanching process. For the conditions evaluated the worst scenario was a total initial peroxidase or lipoxygenase activity of 500 UA/g, 10% of resistant isoenzyme, being 1060 and 180 s, respectively, the heating times necessary to reach an end point of 1 UA/g. Heating times can be significantly reduced if an individual quick blanching process is used.     

A survey of acrylamide precursors in Irish ware potatoes and acrylamide levels in French fries

Reducing sugars (glucose and fructose) and asparagine levels in three varieties of Irish ware potatoes (Rooster, Record and Oilean) on sale in a local supermarket were monitored over an 11-month period. Samples were processed into French fries using conditions similar to those used for home preparation of fries and acrylamide levels in a selection of samples were measured. A wide range of total reducing sugar levels (fructose+glucose) were observed over the course of the study with values ranging from 152-12,286, 301-8812 and 279-7881 μg/g FW for the Rooster, Record and Oilean varieties, respectively. This resulted in high levels of acrylamide in some samples (up to 2970 μg/kg). In comparison to reducing sugars, asparagine contents were relatively constant for the three varieties and no particular trend in asparagine levels was noted. Both fructose and glucose contents of the tubers were positively correlated with acrylamide content (r=0.809, 0.776, respectively, P<0.001). A negative relationship between Hunter L values and acrylamide content of the French fries was observed (r=−0.712, P<0.001) indicating that L values could serve as a convenient and reliable indicator of acrylamide levels in French fries.     

Optimization of frozen sour cherries vacuum drying process

The objective of this research was to optimize the vacuum-drying of frozen sour cherries in order to preserve health-beneficial phytochemicals, as well as textural characteristics. Investigated range of temperature was 46–74 °C and, of pressure, 17–583 mbar, in a new design of vacuum-dryer equipment. The total solids, a_w value, total phenolics, vitamin C, antioxidant activity, anthocyanin content, total colour change and firmness were used as quality indicators of dried sour cherry. Within the experimental range of studied variables, the optimum conditions of 54.03 °C and 148.16 mbar were established for vacuum drying of sour cherry. Separate validation experiments were conducted, under optimum conditions, to verify predictions and adequacy of the second-order polynomial models. Under these optimal conditions, the predicted amount of total phenolics was 744 mg CAE/100 dw, vitamin C 1.44 mg/100 g per dry weight (g dw), anthocyanin content 125 mg/100 g dw, IC₅₀ 3.23 mg/ml, total solids 70.72%, a_w value 0.646, total colour change 52.61 and firmness 3395.4 g. The investigated parameters had a significant effect on the quality of the dried sour cherries.     

Impact of additives to lower the formation of acrylamide in a potato model system through pH reduction and other mechanisms

The impact on acrylamide formation of several additives was investigated as well as the mechanisms behind it. In a potato powder model system, sodium acid pyrophosphate, citric, acetic and l-lactic acid significantly reduced the final acrylamide content, merely due to the lowering of the pH. Free glycine, l-lysine and l-cysteine also lowered acrylamide, while keeping the pH at its original level. l-glutamine increased the formation of acrylamide. A synergistic acrylamide lowering effect was observed, adding citric acid and glycine or l-lysine to the model system. Yet, a combination of these amino acids with acetic acid appeared to induce a restricted antagonistic acrylamide lowering effect. Calcium and magnesium ions induced a supplementary acrylamide reduction in addition to a lower pH of the food matrix. No lowering effect was however observed upon NaCl addition to the model system.     

紫山药淀粉酶解工艺优化及动力学模型研究

以还原糖释放率(DE)为考察指标,考察酶添加量、pH值、温度、时间对紫山药淀粉酶解效果的影响,并采用响应面法对酶解过程中的工艺参数进行优化。通过Lineweaver-Burk和Wilkinson统计法求解米氏常数(Km)和最大反应速度(Vm),建立相应动力学模型。结果表明,紫山药淀粉的最佳酶解工艺条件是α-淀粉酶添加量为23 U/g,酶解温度75℃,酶解p H为5.5,酶解时间77 min,在此条件下,DE值为27.17%;在pH 5.5,75℃条件下,V_m=4.141 mg/(mL·min),K_m=4.329 mg/m L,酶解动力学方程为:v=6.98[S]/(7.94+[S]),R~2=0.996 6。     

Alternative extraction techniques for analysis of acrylamide in food: Influence of pH and digestive enzymes

Acrylamide in food is normally measured as “water-soluble free acrylamide”. However, it is shown that the technique of extraction, according to the method for extraction of dietary fibres or at high pH can affect the results. This has to be accounted for, particularly in the assessment of exposure and in studies of bioavailability and, in the long term, health risk assessment.     

Optimization of microwave frying of osmotically dehydrated potato slices by using response surface methodology

Microwave frying of osmotically dehydrated potatoes was optimized by using response surface methodology. Osmotic dehydration was applied prior to microwave frying in order to reduce oil uptake and to evaluate the effect of osmotic dehydration on quality of microwave fried potatoes. Moisture content, oil content, hardness and color of the fried potatoes were used as quality parameters. Microwave power level (400, 550, 700 W), frying time (1.5, 2.0, 2.5 min) and osmotic dehydration time (15, 30, 45 min) were the independent variables in the study. Osmotic dehydration treatment was conducted using 20% (w/w) sodium chloride solution at 30 °C. Moisture content of the fried potatoes decreased whereas oil content, hardness and ΔE value of potatoes increased with increasing frying time and microwave power level. The increase in osmotic dehydration time reduced moisture content and oil content and increased hardness of fried potatoes. The optimum condition was found as frying at 400 W microwave power level for 1.5 min after 39 min of osmotic dehydration time.     

响应面法优化海地瓜皂苷提取工艺

目的:以海地瓜为原料,开展了海地瓜皂苷的提取工艺研究。方法:在单因素分析的基础上,采用了响应面法分析了乙醇浓度、料液比、提取温度、提取时间等因素对海参皂苷得率的影响,优化获得最佳的海地瓜皂苷提取工艺为:乙醇浓度为79%,提取温度为73.5℃,提取时间为2.75 h,料液比为1∶1.7 g/m L。对海地瓜皂苷的影响由大到小依次为乙醇体积、乙醇浓度、提取时间和提取温度。在该工艺下提取海地瓜皂苷得率为0.378%。与模型预测值一致。结论:响应面分析法确定的提取条件合理,验证值与预测值接近,可以用于海地瓜皂苷的提取工艺优化。      

Optimization of enzymatic degumming process for rice bran oil using response surface methodology

Response surface methodology was used to determine the optimum processing conditions for enzymatic degumming of rice bran oil. Reaction time, enzyme dosage, level of water added and temperature were the factors investigated with respect to phosphorus and free fatty acids contents. A D-optimal design, with four variables and two response functions, was employed to study the effect of the individual variables on the response functions. For each response, second-order polynomial models were developed using multiple linear regression analysis. Applying desirability function method, optimum operating conditions were found to be reaction time of 4.07 h, enzyme dosage of 50 mg/kg, added water of 1.5 ml/100 g and temperature of 49.2 °C. At this optimum point, phosphorous and free fatty acids contents of degummed oil were found to be 8.86 mg/kg and 2.01 g/100 g as oleic acid, respectively.