Effect of freezing/thawing conditions and long‐term frozen storage on the quality of mashed potatoes

The effects of freezing temperature (−80, −40 or −24 °C) and thawing mode (microwave or overnight at 4 °C) on quality parameters of mashed potatoes made from tubers (cv Kennebec) and from potato flakes were examined, as was the effect of long‐term frozen storage on the quality of mashed potatoes. Mashed potatoes were tested for texture profile analysis (TPA) and cone penetration, oscillatory and steady rheometry, colour, dry matter, Brix and sensory analyses. In natural mashed potatoes, TPA hardness and oscillatory parameters showed that processing resulted in a softer product than the fresh control. The parameters were lower in the samples thawed at 4 °C than in those thawed by microwave at all the freezing temperatures used, which may be ascribed to gelatinisation of the starch released from damaged cells. Differences from the freshly prepared product decreased when the samples were frozen at −80 °C and thawed by microwave. No difference was found in sensory acceptability between samples frozen at −80 and −40 °C, which probably reflects the panellists' mixed preferences for air‐thawed versus microwave‐thawed samples. Increasing the time in frozen storage led to a natural mash with a firmer texture, higher L*/b* value and Brix; nonetheless, panellists found the samples at 0, 3 and 12 months of frozen storage equally acceptable. In commercial mash, penetration and oscillatory parameters showed that processing made for a firmer product than the fresh control, probably owing to retrogradation of gelatinised starch. Thawing mode had a significant effect on parameters, which were lower in the samples thawed at 4 °C. The structure and quality of commercial mash was more detrimentally affected by freezing and, therefore, we would not recommend either freezing or frozen storage of this mashed potato in the used conditions. Natural mash made from Kennebec potatoes should be frozen quickly and thawed by microwave in the conditions described to obtain a product more similar to that freshly made. If the samples are frozen by air blasting at −40 °C, the product can withstand frozen storage for one year. Copyright © 2005 Society of Chemical Industry     

Optimisation of freezing process with pressure steaming of potato tissues (cv Monalisa)

Response surface methodology (RSM) was used for determining optimum conditions of the freezing process on pectinesterase (PE) activity, rheological parameters and textural properties in potato tissues. In the process of production of frozen potatoes, the second step of the stepwise blanching prior to freezing was considered as a fixed factor and performed at 97 °C for 2 min as well as the freezing rate in the freezing step itself, which was carried out at −2 °C min⁻¹. The effects of variation in levels of temperature (57.93–72.07 °C) and time (15.86–44.14 min) in the first blanching step on the PE activity were studied using a central composite rotatable design. A Box–Behnken factorial design was used to investigate the effects of simultaneous variation of temperature (60–70 °C) and time (20–40 min) in the first blanching step and steaming temperature (112–122 °C) and time (1–3 min) on rheological parameters and textural properties. Blanching temperature was the independent variable that most influenced either enzymatic activity or rheological parameters. Stationary points showing maximum PE activity had critical temperature and time values of 64.22 °C and 29.37 min before freezing and 64.39 °C and 28.02 min after freezing and steaming of the tissues, and these values were very close to those obtained for some creep compliance parameters. Results show a high correlation between increases in PE activity and tissue firmness below optimum experimental freezing conditions, proving the role of the enzyme as one of the main contributors to the firmness which determines the textural quality of frozen potato tissues. © 1999 Society of Chemical Industry     

Comparative Characterization of Dietary Fibre-Enriched Frozen/Thawed Mashed Potatoes

The potential use of commercial fibres (pea fibre, inulin, and their blends), as fibre-enriching agents in frozen/thawed mashed potatoes was reported. Pea fibre and inulin supplementations conferred hardness and softness to the product, respectively. Differences were attributed to the relationship of the fibre with the potato starch matrix. The association of pea fibre at low concentration (<15 g/kg mashed potatoes) and inulin at high concentration (>45 g/kg) is strongly encouraged to fortify the diet without promoting negative effects on textural and rheological properties of frozen/thawed mashed potatoes or colour and overall acceptability of the resulting products.     

The effect of sample temperature on instrumental and sensory properties of mashed potato products

The effect of sample temperature on texture, firmness and the sensory attributes of fresh and frozen/thawed natural and commercial mashed potatoes was studied. Scanning electron microscopy was used to obtain information on the structure of potato cells and how this is affected by processing. Various parameters were measured and were found to increase at 55 °C, these changes could be related to gelatinisation of the starch remaining in the products. In natural mashed potato, texture profile analysis (TPA) and firmness parameters were lower in the processed than in the fresh samples, indicating a weakening of the structure; this was confirmed by photomicrographs. In commercial mashed potato, TPA parameters measured at 55 and 65 °C and firmness parameters measured at 25 °C were higher in the processed samples, indicating enhanced structural strength; this was confirmed by photomicrographs. Firmness per gram of product was the best instrumental parameter for measuring texture in these products. The results of the different analyses indicated that 55 °C was the preferred temperature for consumption of mashed potatoes.     

Effect of modified starch concentration and freezing and thawing rates on properties of mashed potatoes (cv. Kennebec)

Effects of modified cornstarch concentration, freezing rate and thawing mode on quality properties of mashed potatoes were examined. The product was tested by oscillatory rheometry, instrumental texture profile analysis (ITPA) and cone penetration, colour, dry matter (DM) and sensory analyses. Oscillatory parameters showed that increasing starch concentration resulted in a softer product in which gel strength decreased in direct proportion to concentration in quick‐frozen and microwave‐thawed product. Quick freezing made for firmer mashed potatoes, whereas oscillatory, ITPA and penetration parameters were lower in the samples thawed at 4 °C. Starch concentration and instrumental consistency and firmness were directly proportional to one another. Adding starch at the highest concentration, quick freezing and slow thawing produced a lighter‐coloured mashed potato, although the loss of colour in the processed product was not detected by panellists in the microwave‐thawed samples. DM was higher in the quick‐frozen samples and lower in air‐thawed samples. The factors studied affected different sensory texture parameters but had hardly any effect on attributes perceived during final and residual phases of mastication. Only starch concentration had a significant effect on sensory acceptability, but interactions between factors showed that starch addition followed by quick freezing was judged undesirable by the panellists due to excessive softening. Oscillatory parameters correlated well with sensory texture attributes and proved quite precise. They would therefore appear to be the best test to monitor properties of frozen mashed potatoes. Copyright © 2007 Society of Chemical Industry     

Sensory and Texture Properties of Mashed Potato Incorporated with Inulin and Olive Oil Blends

The effect of adding different ratios of inulin and extra virgin olive oil blends, formulated without (MPA) and with cryoprotectants (MPB), on texture properties of fresh mashed potatoes and frozen/thawed mashed potatoes was studied. Inulin and extra virgin olive oil behaved like soft fillers, but inulin was associated with increased fibrousness and extra virgin olive oil with increased creaminess. In the total dataset and frozen mashed potatoes, frozen/thawed mashed potatoes, and MPA subgroups, component 1 was a contrast between mechanical and surface textural attributes, whereas in MPB samples component 1 was determined by geometrical attributes. Addition of inulin at 30 g/kg and extra virgin olive oil at 45 g/kg is recommended.     

Viscoelasticity and microstructure of inulin-enriched mashed potatoes: Influence of freezing and cryoprotectants

The effect of the addition of inulin (0%, 1.5%, 3%, 4.5% and 6%) on viscoelastic properties and microstructure of fresh and frozen/thawed mashed potatoes (FMP and F/TMP, respectively) formulated without and with added cryoprotectants (kappa-carrageenan (κ-C) and xanthan gum (XG)) was investigated. Results showed that inulin concentration was the factor that set the minor difference among most of rheological properties, firmness and overall acceptability (OA) of the samples, whereas addition of κ-C and XG resulted in main differences between samples. Inulin effect on the thickening of the product was limited, which is mainly ascribed to a high heating temperature reached by the product during manufacture process inducing inulin hydrolysis. FMP samples presented more rigid structure than their F/TMP counterparts, although either inulin concentration or processing had much less significant effect on the viscoelasticity of the mashed potatoes containing cryoprotectants, evidencing the ability of this biopolymer blend to impart freeze/thaw stability.     

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.     

The effect of long-term frozen storage on the quality of frozen and thawed mashed potatoes with added cryoprotectant mixtures

Cryoprotectant mixtures were added to frozen/thawed (F/T) mashed potatoes in the form of amidated low-methoxyl (ALM) pectin and xanthan gum (XG), kappa-carrageenan (κ-C) and XG and sodium caseinate (SC) and XG, and the effect of frozen storage was examined. F/T mashed potatoes without added biopolymers had higher storage modulus G ' after freezing and frozen storage, associated with sponge formation due to amylose retrogradation. Oscillatory measurements indicated weakening of the structure of mashed potatoes without biopolymers and with added κ-C/XG and SC/XG mixtures at the end of storage due to ice recrystallisation, whereas the structure of samples with added ALM/XG mixtures was reinforced by increasing time in storage. Mashed potatoes with added mixtures exhibited water-holding capacity for 1 year. Samples with added κ-C/XG mixtures were more structured, although when both κ-C/XG and SC/XG mixtures were included in mashed potato, very acceptable sensory quality was maintained in usual frozen storage conditions.     

Optimization of Blanching Conditions Prior to Deep Fat Frying of Yam Slices

The effect of low-temperature blanching and frying time at a frying temperature of 170°C on moisture and oil contents, breaking force and colour of yam chips was investigated using response surface methodology to establish the optimum blanching conditions and frying time. A central composite rotatable design was used to study the effects of variation in levels of blanching temperature (60–80°C), blanching time (1–5 min) and frying time (2–6 min) on quality attributes of yam chips. The effect of blanching temperature and frying time was more significant than the time of blanching on the quality attributes. The response variables were fitted to predictive models applying multiple linear regressions. Statistical analysis with response surface regression showed that moisture content, oil content, breaking force and L? (lightness) parameter were significantly (P < 0.05) correlated with blanching temperature and time and frying time. However, the regression equation showed a poor fit for a? and b? respectively. The optimum conditions were a blanching temperature of 70–75°C, blanching time of 4–5 min while frying for about 5 min.     

Enhancement of freezing stability in mashed potatoes by the incorporation of kappa‐carrageenan and xanthan gum blends

BACKGROUND: To ameliorate the detrimental effects of freezing and thawing, blends of κ‐carrageenan (κ‐C) and xanthan gum (XG) were added to frozen/thawed mashed potatoes (F/TM potatoes). Product was tested by textural and rheological measurements, other quality parameters and sensory analyses. The effects of variation in levels of κ‐C (1.5–4.5 g kg^?1) and XG (0.5–2.5 g kg^?1) concentrations were studied. RESULTS: Instrumental measurements and sensory analyses indicated that 4.5 g kg^?1κ‐C and 2.5 g kg^?1 XG provided better thickening. κ‐C provided the appropriate texture, while XG imparted creaminess to the product, which could be associated with an increase in the amount of XG–water interactions. Addition of κ‐C had a major impact on textural properties, gel strength and viscoelastic behaviour, whereas XG influenced steady properties, colour, water‐holding capacity (WHC) and overall acceptability (OA). CONCLUSION: The OA of F/TM potatoes was mostly improved by addition of cryoprotectant blends, which is ascribed to improvement of F/TM potatoes texture by retarding starch retrogradation, increasing WHC, and enhancing the principal characteristics determining consumer acceptance. Creaminess was the most crucial factor for OA of the products. Addition of both polysaccharides at a low concentration (each cryoprotectant at 1.5 g kg^?1) is recommended. Copyright © 2009 Society of Chemical Industry     

Textural Properties and Sensory Quality of Processed Sweetpotatoes as Affected by Low Temperature Blanching

Sweetpotatoes (SP) stored for 9–12 mo after harvest were cut into cylindrical pieces and, following factorial experiments and response surface design, were blanched at 50–80°C for 15–274 min. Instrumental textural properties were measured by uniaxial compression and texture profile analysis. Samples of selected blanching treatments were canned in syrup for textural and sensory evaluations. Both blanching temperature and time had significant effects on firmness. Optimal temperature for maximal firmness retention was about 62°C. For canned SP, the 62°C blanched samples were more intact (2–3-fold) and firmer (2–7-fold) than controls. Sensory texture and overall acceptability were greatest for samples blanched at 62°C for 30 or 45 min before canning.     

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.     

Vitamin C Stability during Preparation and Storage of Potato Flakes and Reconstituted Mashed Potatoes

High performance liquid chromatography with electrochemical detection was used to follow losses of L-ascorbic acid (AsA) in the processing and serving of fortified mashed potatoes. Cumulative losses of AsA were: 56% for adding AsA to freshly mashed potatoes at 251 ppm (wet basis); 82% drum-drying the potatoes; 82% storing the flakes 4.3 months at 25°C., and 96% reconstituting mashed potatoes and holding them 30 min on a steam table. The mashed potatoes at the point of ingestion would contain 10 ppm AsA (wet basis), and one serving size (100g) would provide 2% of the adult RDA. Fortification with equivalent levels of magnesium L-ascorbate 2-mono-phosphate (AsMP) or sodium L-ascorbate 2-polyphosphate (AsPP) gave overall cumulative losses of 20 or 32%, respectively. Such reconstituted mashed potatoes contained 201 ppm and 171 ppm AsA respectively, and one serving would provide about 33% of the RDA of vitamin C.     

A rheological characterisation of mashed potatoes enriched with soy protein isolate

The effect of the addition of soy protein isolate (SPI) (0, 15, 30, 45 and 60 g kg⁻¹) on viscoelastic properties, large deformation measurements and microstructure of fresh (FM) and frozen/thawed (F/TM) mashed potatoes was investigated. Rheological data showed weak gel behaviour for both FM and F/TM potatoes without and with added SPI together with a significant decrease of system viscoelasticity (G′ and G″) with increasing SPI volume fraction, primarily attributed to the no interaction between the amylose/amylopectine matrix and the dispersed SPI particles or aggregates as revealed by scanning electron microscopy (SEM). Micrographs also showed that SPI formed white coarse aggregates. A freeze/thaw cycle produced a more significant decrease in viscoelastic functions, due to superior aggregation of denatured SPI and reduced water activity. In F/TM samples, high correlations between small and large deformation measurements were found. Results may be useful for technological applications in SPI-enriched mashed potatoes.     

Optimization of low-temperature blanching for retention of potato firmness: Effect of previous storage time on compression properties

Low-temperature blanching (LTB) of potatoes (cv. Kennebec), both without further processing and prior to cooking or freezing + cooking, significantly increased firmness retention as measured from compression parameters. The increase in firmness with respect to that of unblanched potatoes diminished in the order: blanched at 60 °C for 60 min and cooked > blanched at 60 °C for 60 min frozen and cooked > blanched at 60 °C for 60 min. Potato tubers were kept in refrigerated storage, and firmness, PME activity and dry matter (DM) content were periodically sampled over a period of 80 days. In the early stages of storage, PME activity lost 40% of its original value after 60 min at 60 °C, indicating that the contribution of starch breakdown products to the firmness of cooked and frozen cooked potatoes predominated over the effect of enzyme activity. With increasing time in storage, PME activity measured in the fresh tissue increased by 95% of its original value after 35 days; this resulted in changes in the pectic polymers which made for a firmer texture and different PME behaviour versus LTB temperature and time. A central composite rotatable design was used to study the effects of variation in levels of temperature (52.93–67.07 °C) and time (31.72–88.28 min) on compression parameters and PME activity. Stationary points showing maximum mechanical resistance had critical temperatures and times in the ranges of temperature (58–60 °C) and time (66–75 min) used for each independent variable. Results show a high correlation between PME activity and tissue firmness, suggesting that the contribution of the changes in the composition of the cell wall to the firmness of frozen cooked potatoes increased with increasing time in storage and reached a maximum in the intermediate stages of storage (35 days). Engineering stress (_u) proved to be the most appropriate compression parameter for detecting the firming effect that the PME activity produced on the frozen-cooked potato tissues as a consequence of LTB under these conditions.     

新鲜鱿鱼超高压杀菌工艺试验

为确定新鲜鱿鱼超高压杀菌工艺的最佳工艺参数,以杀菌压力、保压时间、漂烫温度为条件,设计了新鲜鱿鱼超高压杀菌试验。试验结果表明,90℃漂烫10 min,在400 MPa压力下保压10 min,此为新鲜鱿鱼超高压杀菌的最佳工艺条件。     

送风参数对马铃薯泥冷冻特性的影响

利用Fluent软件建立马铃薯泥三维鼓风冷冻数值模型,研究冷冻时间对送风温度和速度的敏感程度,分析不同位置马铃薯泥冷冻条件和冷冻时间的不均匀度随送风参数的变化规律。结果表明,送风温度的改变对冷冻时间的影响比送风速度大。送风温度不变,随着送风速度的增大,马铃薯泥周围风速的不均匀度逐渐增大,温度的不均匀度逐渐减小,冷冻时间的不均匀度和中心温度的不均匀度随送风速度的增加呈现先减小后增大的趋势,送风速度为6 m/s时,二者最小。同一送风速度条件下,送风温度越低,马铃薯泥周围温度的不均匀度越小,中心温度的不均匀度越大。经验证,模拟结果与实验结果吻合较好,冷冻时间相对误差为3.27%,温度的平均绝对误差为0.79 K,均方根误差为2.11K。     

漂烫对速冻苹果质地的影响

采用质地多面分析（TPA）试验方法,研究了速冻苹果不同漂烫过程中的漂烫时间、漂烫温度、料液比对质地的影响,并对其过氧化物酶（POD）活性、感官品质的变化以及其硬度、内聚性、回复性、弹性和咀嚼性等相关性进行了研究。结果表明,漂烫对速冻苹果质地有显著影响,适度漂烫在其速冻加工中至关重要,最佳漂烫工艺为漂烫时间4～5 min、漂烫温度87～92 ℃,料液比为1∶10～1∶12（g∶mL）。     

Effect of Processing Methods on Physical,Chemical, Rheological,and Sensory Properties of Okra (<Emphasis Type="Italic">Abelmoschus esculentus</Emphasis>)

Effects of freezing/thawing, sun drying, solar drying, and foam-mat drying on physical, chemical, rheological, and sensory attributes of okra were investigated. Average poured bulk and tapped bulk densities of sun-dried, solar-dried, and foam-mat-dried okra were 800 and 950, 715 and 765, 355 and 367 kg/m³, respectively. Minimum and maximum porosity of sun-dried, solar-dried, and foam-mat dried okra were 55.70% and 62.60%, 50.06% and 53.30%, 60.90% and 62.87%, respectively. Sun-dried and solar-dried okra showed higher L*, a*, and chroma values than frozen/thawed and foam-mat-dried okra. Within a temperature range of 80–40 °C, viscosity of fresh, frozen/thawed, foam-mat-dried, solar-dried, and sun-dried okra were 0.055–0.080, 0.055–0.075, 0.050–0.073, 0.005–0.065, and 0.005–0.022 Nsm⁻², respectively. Sensory evaluation showed no significant difference (p < 0.05) between fresh, frozen/thawed, and foam-mat dried okra in color, aroma, and overall acceptability. Sun-dried and solar-dried okra were significantly poorer (p < 0.05) in color, aroma, taste, and overall acceptability.