Crust morphology and crispness development during deep-fat frying of potato

Crust formation is an important factor in determining the crispness of French fries. This study aimed at unravelling detailed structural and textural properties of the crust in relation to crispness during frying as a function of the process temperature and time. X-ray tomography showed a larger overall pore volume at higher frying times, while a lower final moisture content mainly resulted in an increase in the amount of large pores. Texture analysis revealed that the increase in porosity, due to the increased formation of pores, results in a more crispy behaviour after frying with oil of up to 180 °C. At temperatures above 180 °C crispness is actually found to decrease again, which is explained by the increased plastic behaviour of the crust. This may be related to the reduced glass transition temperature of the crust because of increased sugar degradation at a very high temperature.     

On the mechanism by which oil uptake decreases crispy/crunchy behaviour of fried products

A large problem for fried snack products with a crispy crust and a soft moist interior is that the crust often loses its crispy character fast, in the order of 3–20 min. As known during cooling of these snacks adherent oil will be sucked into the crust. The presence of oil in a cellular solid crispy material was found to affect the sound emitted on fracture dramatically, while it did not affect mechanical characteristics at least for shorter ageing times. Both the number of sound events and the acoustic energy released during fracture decreased. This could be explained by reflection of emitted sound at the oil–air interface. Both the smaller number of acoustic events and the lower loudness will cause a decrease in crispy perception of the crust and in that way oil uptake during cooling of fried snacks can explain their fast decrease in crispness after frying.     

2种加工方法对美国引进薯条加工型品种感官品质的影响

目的以从美国引进的薯条加工型品种或品系为实验对象,比较漂烫预油炸加工法和直接油炸加工法2种加工方法对其感官品质的影响。方法采用漂烫预油炸加工法和直接油炸加工法对其加工,采用感官评价的方法比较2种加工方法对薯条感官品质的影响。结果漂烫预油炸法与直接油炸法相比,在外观指标和总体评分上均有显著性差异(P0.05),而在其他指标均无显著性差异,且2种方法对外观、湿度、外壳和内部表现4个指标的影响趋势大致相同。结论漂烫预油炸方法与直接油炸方法相比,改进了外观色泽,但并未改变薯条的其他加工性状,在加工薯条品种筛选的过程中推荐使用该方法。     

Frying Oil Temperature: Impact on Physical and Structural Properties of French Fries During the Par and Finish Frying Processes

The physical, mechanical, and structural changes in French fries at different frying temperatures (170, 180, and 190 °C) during par and finish frying were investigated. The experimental frying process includes blanching, par frying, freezing, and finish frying at the point of consumption. Par frying temperature had a greater effect on moisture reduction than on processing time with the greatest moisture loss at 180 °C after 160 s. At 180 °C, fries had the highest total oil uptake (29.56 % wb). Frying caused a significant change in color with the greatest effect at 190 °C. Micro-CT scan images showed structural changes in French fries over the course of the frying process. Frying time increased the volume of the pores relative to the size of the crust, and this was positively correlated with the hardness and shear cutting force. Overall, within the range of frying conditions studied, the higher temperature (190 °C) resulted in the lowest amount of oil uptake and the crispiest texture.     

Fat Uptake in French Fries as Affected by Different Potato Varieties and Processing

ABSTRACT: The uptake of lipid into French fries was investigated using two varieties of potato ('Russet Burbank' and 'Agria') and the New Zealand sweet potato, Ipomoea batatas , (kumara). The variety of potato used had a significant effect on lipid uptake, with 'Agria' having the lowest lipid content. The different cellular structures may have affected the fat uptake in the French fries by influencing either the loss of moisture during finish-frying or the damage done to the original anatomy during processing before pre-frying. The French fries that had undergone frozen storage had a higher amount of lipid contained in their inner core than did those that had been either chilled or prepared freshly for frying.     

Bread crispness and morphology can be controlled by proving conditions

Bread crust crispness is lost when water migrates from crumb to crust during storage. To what extent water migration is influenced by morphology is not known. Therefore, the effect of crispy rolls morphology on crust crispness was studied. Crispy rolls were prepared at three proving volumes: 300 mL (short proving), 500 mL (control) and 800 mL (long proving). X-ray microtomography was used to characterize morphology.Water transport from crumb to crust was determined. Short proved crispy rolls showed lower rate of crust water uptake while longer proved rolls showed faster uptake during cooling down. Sensory analysis revealed higher crispness for short proved crispy rolls after the same storage time at low RH. We hypothesize that shorter proved crispy rolls with finer crumb morphology, more closed structure, smaller gas cells with less gas cells interconnections and a thicker crust have a significant positive effect on water uptake kinetics and crispness retention.     

Deterioration of olive,corn and soybean oils due to air,light, heat and deep-frying

To follow the relative rate of oxidative deterioration of edible oils, refined olive, corn and soybean oils were analyzed periodically for their peroxide value (PV), p-anisidine value (p-AV) and iodine value (IV) following exposure to air and air–light for 30 days. Changes in the above values of the oils were also examined and after being used for deep frying of French fries at 180 °C for varying periods of time i.e. 30, 60 and 90 min PV and p-AV values increased in the order, deep frying > air–light exposure > air exposure, while the values with respect to the oils increased as soybean > corn > olive. Decreases in IV followed the same pattern, i.e. deep frying > air–light > air and soybean > corn > olive. %Free fatty acid increased with increase in time of deep-frying. Deep-frying of French fries in corn oil was also carried out in presence of caffeic, ferulic, vanillic acid and crude tea extract as antioxidants. All antioxidants effectively reduced the oxidation rate in the oil as detected by decreases in PVs and p-AVs and relatively low reduction rates in IVs for all the frying times. The order of antioxidative activity was caffeic acid > vanillic acid > ferulic acid > tea extract. Variation in %FFA of corn oil due to variation in nature of fried food was also analyzed. %FFA of the oil used for deep frying of chicken drum sticks were higher than the values of the oil used for deep-frying of French fries.     

Effects of Processing Conditions on Qualities of Rice Fries

ABSTRACT Two rice flour mixtures, 2 extruding temperatures, and 2 insert sizes were used to develop rice fries. The extruded material was cut into pieces 7 to 8‐cm long, prefried in rice oil at 180°C for 20 s, and kept frozen until final frying for another 70 s. The rice fries were evaluated 5 min and 10 min after final frying for their lipid, moisture, and instrumental texture characteristics. Extruding temperature, rice cultivar, and insert size were significantly related to fat content, moisture, hardness, and fracturability values. A mixture consisting of 80:20 (waxy:long‐grain), and extruded at 70 °C using a 6 mm insert, 5 min after frying, gave a texture profile analysis value for hardness, cohesive‐ness, and gumminess values comparable to commercial potato French fries. The rice fries made by the process also had less than 50% fat than potato fries.     

QUALITY COMPARISON OF FRENCH FRY STYLE POTATOES PRODUCED BY OVEN HEATING, IMMERSION FRYING AND CONTROLLED DYNAMIC RADIANT HEATING

The effect of finish heating method (oven heating, immersion frying and controlled dynamic radiant (CDR) heating) on mechanical properties, color and sensory properties of par‐fried French fries was evaluated. Peak breaking force was highest for CDR‐heated French fries. An equivalent b value (yellowness) for the crust of immersion‐fried and CDR‐heated French fries was found by using color analysis. Sensory evaluation indicated overall acceptability of CDR‐heated French fries equivalent to immersion fried‐French fried potatoes. Finish heating of par‐fried French fries using CDR heating showed promise to produce a reduced‐fat fried product, as well as an alternative process to traditional immersion finish frying.     

半干鲢鱼片油炸工艺研究

以鲢鱼为原料,研究油炸前鱼片含水量对油炸产品、油炸条件对鲢鱼片脱水速率、吸油率、产品质构的影响。结果表明,油炸最适条件为180℃,油炸约4.5min,产品最终水分含量在40%左右。油炸前鱼片含水量控制在65%左右,能有效降低油炸时鱼片的吸油且能得到品质较好的鱼片。     

On the Possibility of Nonfat Frying using Molten Glucose

Fried products impose a health concerns due to considerable amount of oil they contain. Production of snack foods with minimal oil content and good management of oil during frying to minimize the production of toxic compounds continue to be challenging aims. This paper aims to investigate the possibility of producing a fat‐free food snack by replacing frying oil with a nonfat medium. Glucose was melted and its temperature was then brought to 185 °C and used to fry potato strips, to obtain a product referred here as glucose fries. The resulting product was compared with French fries prepared conventionally under conditions that resulted in similar final moisture content. The resulting products were also examined for crust formation, texture parameters, color development and glucose content. Stereo microscope images showed that similar crusts were formed in the glucose fries and French fries. Texture parameters were found to be similar for both products at 5 and 2 mm penetration depth. The maximum hardness at 2 mm penetration depth was also similar for both products, but different from cooked potato. The color development that characterized French fries was also observed in glucose fries. The glucose content in glucose fries was found to be twice the content of French fries, which is to be expected because glucose absorbed or adhered to the surface. In conclusion, glucose fries, with similar texture and color characteristics to that of French fries, can be prepared by using a nonfat frying medium.     

Structural changes and shrinkage of potato during frying

Summary Light microscopy was used to study changes in cell size, blister formation and crust evolution during potato frying. Frying experiments with both French fries and crisps of different thickness (1–5 mm) were performed at temperatures of 140 and 180 °C. Thickness, volume and density changes were also measured. The formation of crust in French fries starts after the potato surface reached approximately 103 °C, and then the crust thickness increased linearly with the square root of frying time, this increase being faster at 180 °C. The potato volume decreased during frying, although in the late stages the volume may increase because of oil uptake and cell separation caused by entrapped water vapour. Shrinkage was adequately described by the Weibull model with a residual value, with shrinkage rate increasing with temperature and decreasing with potato thickness. The residual volume was not affected by temperature (65% for French fries and 59–30 for crisps, depending on thickness). Volume appeared to decrease mainly as the result of water loss, except for very low water content, and thus potato density changes were very small.     

Evolution of mechanical and optical properties of French fries obtained by hot air-frying

The aim of this study was to analyse the influence of frying technique (air-frying and deep oil-frying) and type of pre-treatment (freezing and blanching) on the evolution of mechanical and optical properties of French fries. The results showed that the chromatic parameters, a* and b*, experimented an increase regardless of the frying method. The increase in a* was significantly higher in deep-oil frying as a result of Maillard's reactions. The texture analysis reported a first stage of initial softening related to starch gelatinization followed by a second stage where the maximum force increased due to the gradual formation of a crust, both stages being faster in deep-oil frying. Pre-frozen potatoes presented the highest value of maximum force parameter independent of the type of frying.     

Effects of the sound of the bite on apple perceived crispness and hardness

The effects of the manipulation of the sound produced while biting into apple samples, a non-dry food, was investigated. In Experiment 1, participants rated the perceived crispness of flesh cylinders obtained from three apple cultivars differing in their texture profile: ‘Renetta’ (white ‘Renetta Canada’), ‘Golden’ (‘Golden Delicious’), and ‘Fuji’. Participants might hear the veridical sounds they made when biting into an apple cylinder without any frequency adjustment (0 dB filter) or with high frequencies attenuated (either by −12 dB or by −24 dB). Perceived crispness was significantly lower when any of the reductions were applied than when no filter (0 dB) was used. In Experiment 2, new participants rated both crispness and hardness of ‘Renetta’ and ‘Fuji’ cylinders. The sound of the bite could be unfiltered (0 dB), reduced in its high frequencies (−24 dB), or globally reduced (the microphone was switched off). Crispness, again, was perceived as significantly lower with any of the sound reductions. Interestingly, perceived hardness was significantly affected by the sound information as well: Hardness was rated as being significantly lower when a global sound reduction was applied than when the sound was unfiltered. We demonstrated, for the first time, that sound information plays an important role even for the evaluation of hardness, a property believed to be primarily oral/mechanical.     

Effect of frying variables on French fry properties

This work focuses on the effect of frying variables (repeated frying, potato‐to‐oil ratio, potato distribution in the fryer, oil type and potato variety) on French fry properties (water content, oil content, crust thickness and shrinkage). Furthermore, the rate of change in French fry properties during a frying batch is investigated. The temperature was acquired in several positions within the oil and the potato. It was found that when repeated frying was conducted up to regulation limits for frying oil use, the examined French fry properties were not significantly affected. On the contrary, the potato‐to‐oil ratio, potato distribution and potato variety significantly affected the water content of French fries. The most significant changes occurred during the first 1–2 min of a frying batch. According to the temperature measurements, the crust‐core front continued to advance after this first frying period. However, there was no observable crust thickness increase; this was attributed to crust shrinkage.     

Rice Fry Texture as Affected by Gum Application and Mechanical Perforation

ABSTRACT: This study was designed to evaluate the effects on rice fries with respect to lipid and moisture contents, as well as instrumental texture characteristics as a result of either coating with a water-soluble gum solution or processing with a mechanical pinhole. The rice fries were formulated from 2 different rice flour mixtures. Statistical analyses showed that gum application significantly decreased fat absorption during frying and retained more moisture. The incorporation of a pinhole decreased moisture and increased fat contents. Increasing gum application lowered hardness and fracturability values. Gum application improved the overall appearance, as well as decreased popping and blistering of fries during final frying.     

Effect of pre-drying and par-frying conditions on the crispness of French fries

An experimental design was used to study the effect of pre-drying (to 10, 15 and 20% weight loss) and par-frying conditions (160, 170 and 180 °C) on the crispness of French fries. Par-frying time was adjusted with a software program to obtain equal moisture content and internal texture for all samples. Crispness was evaluated with a sensory panel. Furthermore, samples were analysed with a texture analyser and with confocal scanning laser microscopy (CSLM). Par-frying at 180 °C resulted in a crispier product than at 160 and 170 °C. Pre-drying to 20% weight loss lead to blisters and reduced crispness in comparison with pre-drying to 10 and 15% weight loss. Instrumental texture measurements showed a good correlation with sensory crispness. Large differences in cell structure, such as blisters, could be observed with CSLM. CSLM was useful to explain results from the instrumental and sensory texture evaluation.     

面糊组分对预油炸微波复热鸡米花品质及水分分布特性的影响

针对鸡米花在微波复热过程中水分“外迁”和油分“外浸”造成脆性降低的问题,研究不同面糊组分,羟丙基羧甲基纤维素（hydroxypropyl methylcellulose,HPMC）和麦芽糊精对预油炸及微波复热后鸡米花含油量、含水量及分布、脆性、颜色、感官品质的影响,以期提高鸡米花微波复热后的脆性及品质特性。结果表明,面糊中添加2%?HPMC和6%麦芽糊精显著降低了微波复热后鸡米花外壳中含水量的增加以及内芯肉中含水量的减少（P＜0.05）,同时使内芯肉T22向快弛豫方向移动,降低了自由水的移动性,同时微波后A22显著高于对照组（P＜0.05）,抑制微波过程中内芯肉中自由水向外壳的迁移,从而保证微波复热后鸡米花外壳脆性和内芯肉多汁性;添加2%?HPMC、6%麦芽糊精及两者复配的微波复热鸡米花外壳脆性较对照组均显著提高（P＜0.05）;但添加2%?HPMC的鸡米花外壳硬度最大,添加6%麦芽糊精的鸡米花含油量最高（P＜0.05）。当面糊中同时添加2%的HPMC和6%的麦芽糊精时,鸡米花经微波后其外壳脆性最好,硬度适中且无油腻感。该研究结果为裹粉类微波食品脆性及品质的改善提供了数据基础。     

Effect of Pre-Drying and Hydrocolloid Type on Colour and Textural Properties of Coated Fried Yam Chips

The effect of pre-drying and coating on colour and texture of yam chips were investigated. The colour parameters studied were lightness index (L*), hue angle (h) and browning index (BI). Peak force (PF) of penetration was observed for texture. Coating pick-up (amount of coating adhering to the samples) prior to frying was determined and moisture content of fried samples was also determined. The type of hydrocolloids used in the coating formulation had significant (p < 0.05) effect on coating pick-up, initial moisture content and texture of the chips; while samples that were not pre-dried had higher pick-ups and moisture contents. Pre-dried samples were darker brown in colour and harder in texture than samples that were not pre-dried as evidenced by their higher browning index and peak force values, respectively, thus enhancing the colour and texture of the chips.