Mashed Potatoes Research Articles

Optimization of pulsed microwave heating

A simulation model was used to optimize pulsed microwave heating of precooked mashed potato cylinders of 82.7% moisture content. The experimental variables were: (1) sample radius: 2.4, 2.8 and 3.2 cm (or 1.5, 1.75 and 2.0 times the penetration depth of microwave radiation), (2) temperature rise during microwave power-on constraint (Δ T on): 20 and 15 °C, (3) temperature drop during microwave power-off constraint (Δ T d): 5 and 3 °C lower than Δ T on, (4) total processing time (<1000 s) and (5) average sample temperature (60 °C). The evaluation showed that the 2.4–2.8-cm radius samples were heated uniformly and efficiently. The Δ T on constraint is very critical for optimum pulsed microwave heating; Δ T on = 20 °C was a better choice than Δ T on = 15 °C. Δ T d constraint affects the total processing time for a large sample more significantly than for a small sample. The total processing time depends on Δ T on, Δ T d, and sample radius. In the case of 2.4-cm radius samples (1.5 times the penetration depth) with Δ T on(Δ T d) = 20(3) °C constraint, the pulsed microwave energy can heat the mashed potato sample to an average temperature of 60 °C in 336 s. This was the most efficient process among all evaluated conditions with respect to total processing time.

The effect of low‐temperature blanching on the quality of fresh and frozen/thawed mashed potatoes

SummaryThe effect of low‐temperature blanching (LTB) prior to cooking on colour, textural, firmness and oscillatory parameters, sensory attributes and overall acceptability of either fresh or frozen/thawed mashed potatoes was studied using response surface methodology (RSM) to establish the optimum temperature and time for blanching in both types of mashed potatoes. A central composite rotatable design was used to study the effects of variation in levels of blanching temperature (57.93–72.07 °C) and time (15.86–44.14 min) on the quality parameters. Stationary points showing maximum thickening had critical temperatures (approximately 67–69 °C) and times (approximately 26–30 min) in the ranges of temperature and time used for each independent variable for both fresh and frozen/thawed mashed potato. Results showed a high correlation between structural reinforcement and overall acceptability under optimum experimental blanching conditions. This demonstrates the potential of this experimental approach in terms of tailoring physical properties to predetermined levels in order to meet consumer preferences in mashed potatoes, and of altering the changes that occur after freezing and thawing.

Influence of different processing methods on the glycemic index of potato (Nicola)

Potato is a food which yields very variable glycemic responses. It makes a major contribution to total starch intake and the share of processed potato products is growing. The aim of the study was to determine the effects of processing and storage on the glycemic indices (GIs) of industrially processed potato products. Two groups (11 and 10 volunteer subjects) attended a glucose tolerance test and glycemic response test of 4 and 3 processed potato products, respectively. GIs of different potato products were calculated for each subject using their own glucose tolerance test and glycemic responses for test meals and averages calculated for each product. GIs of freshly prepared potato products were high: steam boiled potatoes 104±39, oven-baked casserole 95±30 (carbo-peeled sliced potato) and mashed potatoes 106±42. GIs of cooled and cold stored potato products were intermediate, potato cubes served cold 76±32 and cooled, reheated oven-baked casseroles 73±25 (carbo-peeled sliced potato), 75±17 (carbo-peeled mashed potato) and 81±28 (steam-peeled mashed potato). Cooling and cold storage decreased GIs significantly (steam boiled potatoes vs. steam boiled potato cubes ( P = 0.01 ), freshly served casserole made of sliced potatoes vs. casserole cooled, cold stored and reheated P = 0.01 ). Conclusion Cooking method, peeling method, or slicing or mashing did not affect the GIs. Cooling and cold storage, despite reheating, lowered GIs of potato products by about 25%.

Understanding Factors Affecting near Infrared Analysis of Potato Constituents

Most factories belonging to the Dutch company Avebe are working on products based on potato starch. More recently, there has been a strong development in the extraction and use of other potato constituents (i.e. protein, fibres). At present, farmers are paid on the outcome of the “under water weight” measurements, a procedure prescribed by the EC to predict the starch content. However, since there is an outlet in the market, the company is also willing to pay out according to the protein content. The introduction of near infrared (NIR) spectroscopy as a fast quality control technology may be of great help in reaching this objective. NIR, placed either at-the-gate or at-line or in-line at plant level, will contribute to the setting up of a more objective payment method which will, in turn, contribute to an improvement in the financial situation of the farmers and also to better control of the complete manufacturing process. A total of 275 mashed potatoes were analysed by using a FT-NIR (ABB Bomem MB160D) spectrometer and calibration equations were developed to predict dry matter (DM), starch (ST), crude protein (CP) and recoverable protein (RP) content. The equations developed for the prediction of DM and ST presented an accuracy and precision acceptable for routine analysis according to their RPD values (4.2 and 3.1, respectively). However, the equations obtained for CP and RP presented a low predictive ability ( RPD ≈ 1.5). A discriminant analysis performed by using PLS2 regression correctly classified 87.5% of mashed potato samples in groups of low (&lt; 14 mg g−1) and high (≥ 14 mg g−1) protein content. A feasibility study with entire potatoes and a diode array spectrometer (Corona 45 VIS+NIR) was carried out and the preliminary results show great expectations concerning further implementation of NIR technology at the factory gate. However, further research and demonstration activities are needed before application will become possible.

Characteristics and Modeling of Escherichia coli Growth in Pouched Food

Characteristics of the growth kinetics of Escherichia coli cells in pouched mashed potatoes under various conditions were studied with a mathematical model. Bacterial cells were inoculated in sterile mashed potatoes and then sealed in vinyl pouches, in which a very small amount of air was included. The growth curves of cells in the pouched mashed potatoes at constant temperature (12-34 degrees C) were sigmoidal with time on a semi-logarithmic plot and were successfully described with a new logistic model recently developed by us. The rate constant of growth showed a highly linear relationship to the temperature with the square-root model, and the lag period was longer at lower temperatures. The growth curve in glass tubes containing a large volume of air was similar to that in pouches, showing that the rate of growth was not affected by the volume of the surrounding air. The growth curves in pouched mashed potatoes were very similar to those in nutrient broth or on the surface of nutrient agar, which we previously reported. These results suggested that the growth kinetics of the bacterial cells under various conditions of rich nutrition might be almost identical, and can be described with a simple growth model like ours.

Model Comparison for Escherichia coli Growth in Pouched Food

We recently studied the growth characteristics of Escherichia coli cells in pouched mashed potatoes (Fujikawa et al., J. Food Hyg. Soc. Japan, 47, 95-98 (2006)). Using those experimental data, in the present study, we compared a logistic model newly developed by us with the modified Gompertz and the Baranyi models, which are used as growth models worldwide. Bacterial growth curves at constant temperatures in the range of 12 to 34 degrees C were successfully described with the new logistic model, as well as with the other models. The Baranyi gave the least error in cell number and our model gave the least error in the rate constant and the lag period. For dynamic temperature, our model successfully predicted the bacterial growth, whereas the Baranyi model considerably overestimated it. Also, there was a discrepancy between the growth curves described with the differential equations of the Baranyi model and those obtained with DMfit, a software program for Baranyi model fitting. These results indicate that the new logistic model can be used to predict bacterial growth in pouched food.

Glycaemic index and glycaemic load in the diet of healthy schoolchildren: trends from 1990 to 2002, contribution of different carbohydrate sources and relationships to dietary quality

Despite intense discussion of the glycaemic index (GI) and glycaemic load (GL) concepts, data on the GI or GL levels in the diet of children are scarce. The present analysis determined trends in the levels of GI or GL of healthy children from 1990 to 2002 and examined the contribution of carbohydrate (CHO) sources to the overall GL, and the relationships of the GI and GL to the overall dietary quality. The analysis includes three cohorts of participants from the Dortmund Nutritional and Anthropometrical Longitudinally Designed study, aged 7-8 years in 1990 (n 53), 1996 (n 46) and 2002 (n 56). A GI value was assigned to all CHO foods recorded over three consecutive days. In comparison with 1990, 7-8-year-old children in 2002 had slightly higher GI (56.5 v. 55.1 %; P=0.03) and GL (17.5 v. 16.7 g/MJ; P=0.04) levels. In all three time periods the combined contribution of the 'tolerated food groups' (i.e. sweets, soft drinks, cakes and cookies, and salty snacks) to the overall GL exceeded that of bread and rolls (1990, 31 v. 24 %; 1996, 29 v. 31 %; 2002, 28 v. 25 %). Conversely, rice and fried or mashed potatoes had only a minor impact. Children in the lowest GI tertile, but not those in the lowest GL tertile, had a better nutrient profile and a more favourable food choice. In conclusion, partial replacement of high-GI 'tolerated food groups' for low-GI foods would help to reverse the slight recent increases in GI and GL, and to improve the overall dietary quality of 7-8-year-old children.

An outbreak of staphylococcal food poisoning caused by enterotoxin H in mashed potato made with raw milk

Mashed potato made with raw bovine milk was suspected to have been the source of a food poisoning outbreak. Almost 8 × 10 8 Staphylococcus aureus CFU g −1 were detected in the mashed potato. S. aureus was also found in bulk milk from the farm that had supplied milk for the mashed potato. Isolates from mashed potato and bulk milk were positive for the gene encoding staphylococcal enterotoxin H ( seh), and the corresponding protein toxin, SEH, was detected by ELISA in the mashed potato. Production of SEH by S. aureus isolates from mashed potato ( n = 4) and bulk milk ( n = 4) was also demonstrated by ELISA. Sequencing of seh from one mashed potato isolate and one bulk milk isolate confirmed that the gene was a variant seh, and that the genes in both isolates were identical. Macrorestriction of chromosomal DNA with Sma1 followed by pulsed-field gel electrophoresis of seh-positive S. aureus from mashed potato and bulk milk revealed indistinguishable banding patterns between isolates from both sources. It seems likely that raw bovine milk used in the preparation of mashed potato contained S. aureus that subsequently produced sufficient SEH in the mashed potato to cause food poisoning.

Controlled Low-Temperature Vacuum Dehydration and Tunnel Drying: A Comparative Study

Controlled low-temperature vacuum dehydration (CLTVD) and tunnel drying (TD) processes were applied to mashed potatoes and the quality of the dried products was compared for both processes. Slabs of different thickness (0.26, 0.52 and 0.78 mm) were prepared. CLTVD was carried out at a low temperature avoiding freezing the product, at absolute pressure of 0.67, 1.00 and 1.33 kPa. For the TD experiments air temperatures were 40, 50 and 60° C. CLTVD and TD processes were compared using engineering and quality parameters (bulk density, water adsorption and total color difference). During the constant-rate drying period 40 to 70% of moisture was removed. The best quality product was generated at 0.26 mm, 0.67 kPa for CLTVD and 0.26 mm, 40° C for TD. For these treatments, the flux of mass was 7.8 3 1025 and 3.3 3 1024 kg m22s21 for CLTVD and TD, respectively. The mass transfer coefficient was 6.2 3 1026 kg m22s21 ΔY21 for CLTVD and 3.6 3 1022 kg m22s21 ΔY21 for TD. The falling-rate drying period was divided into three sub-periods. The effective diffusivity coefficient ranged from 1.1 3 10211 to 4.8 3 10211 m2/s and from 4.2 3 10211 to 9.6 3 10211 m2/s for CLTVD and TD, respectively. A change in water transport mechanism was achieved and both processes were controlled by mass transfer; internal and external mass transfer resistances were higher for CLTVD than for TD. CLTVD yields a product with lower shrinkage and a color closer to the white standard than the products obtained by TD. CLTVD may be considered as a potential alternative for drying of temperature-sensitive materials.

Kinetics of chemical marker M-2 formation in mashed potato—a tool to locate cold spots under microwave sterilization

Chemical marker M-2 (4-hydroxy-5-methyl-3(2H)-furanone) can be used as a tool to evaluate heating patterns of foods in microwave sterilization. This research studied the kinetics of the M-2 formation in mashed potato as influenced by temperature and salt content. Mashed potato (83.12% moisture content) with 1.5% d-ribose was heated in the capillary tubes at four temperature levels. Chemical marker M-2 yield was obtained using high performance liquid chromatography. Formation of M-2 in plain mashed potato was a first-order reaction. The rate constant changed with temperature following an Arrhenius relationship. For kinetic parameters estimation, one-step non-linear regression was the best followed by modified two-step regression. Amino acid was the limiting element in the formation M-2 in mashed potato. The salt content of 0–1% had no influence on the chemical marker yield. Addition of l-lysine more than 1% resulted in too dark color after sterilization treatments.

The glycemic index of foods influences postprandial insulin-like growth factor–binding protein responses in lean young subjects

Growth in normal and malignant tissues has been linked to hyperinsulinemia and insulin-like growth factors (IGFs). We hypothesized that IGF and IGF-binding protein (IGFBP) responses may be acutely affected by differences in the glycemic index (GI) of foods. We compared the postprandial responses of IGFs and IGFBP to 2 foods of similar macronutrient composition but with greatly different GIs-pearled barley (GI: 25) and instant mashed potato (GI: 85). Ten young lean subjects consumed 50-g carbohydrate portions of the 2 foods or water (extended fast) in random order after an overnight fast. Capillary blood was collected at regular intervals over 4 h for measurement of blood glucose, insulin, and components of the IGF system. Serum IGFBP-1 declined markedly after both meals, but the mean (+/-SEM) change at 4 h was significantly (P < 0.01) more prolonged after the low-GI meal (-55 +/- 20 ng/mL) than after the high-GI meal (-13 +/- 15 ng/mL). Conversely, the change in serum IGFBP-3 concentration at 4 h was significantly (P < 0.05) higher after the low-GI meal (251 +/- 102 ng/mL) than after the high-GI meal (-110 +/- 96 ng/mL); the same pattern was observed at 2 h. Changes in IGFBP-2, free IGF-1, and total IGF-1 responses were minimal and did not differ significantly from those during the 4-h fast. Acute changes in IGFBP-3 after low-GI and high-GI foods may provide a biologic mechanism linking cell multiplication with greater consumption of high-GI carbohydrates.

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

AbstractThe 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

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

SummaryThe 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.

Glycemic index of potatoes commonly consumed in North America

Objective To determine the effect of variety and cooking method on glycemic response and glycemic index of common North American potatoes. Design Study 1: subjects consumed 200 g Russet or white potatoes that were either (a) precooked, refrigerated, and reheated (precooked) or (b) cooked and consumed immediately (day-cooked). Incremental area under the curve was determined. Study 2: subjects consumed 50 g carbohydrate portions of white bread or potatoes (six different varieties and two different cooking methods). Glycemic index values were calculated. In both studies meals were consumed after a 10- to 12-hour overnight fast and finger-prick capillary-blood glucose was measured before and at intervals for 2 hours after consumption. Subjects The study groups were as follows: Study 1 comprised four men and six women, aged 20 to 44 and Study 2 comprised 11 men and one woman, aged 18 to 50. Statistical analyses Repeated measures analysis of variance with Newman-Kuels to protect for multiple comparisons (criterion of significance two-tailed P<.05). Results Study 1: Precooked Russet potatoes elicited lower area under the curve than day-cooked ( P<.05), while precooking had no effect on boiled white potatoes. Study 2: The glycemic index values of potatoes varied significantly, depending on the variety and cooking method used ( P=.003) ranging from intermediate (boiled red potatoes consumed cold: 56) to moderately high (roasted California white potatoes: 72; baked US Russet potatoes: 77) to high (instant mashed potatoes: 88; boiled red potatoes: 89). Conclusions The glycemic index of potatoes is influenced by variety and method of cooking and US Russet potatoes have only a moderately high glycemic index. Individuals who wish to minimize dietary glycemic index can be advised to precook potatoes and consume them cold or reheated.

Potato glycoalkaloids and adverse effects in humans: an ascending dose study

Glycoalkaloids in potatoes may induce gastro-intestinal and systemic effects, by cell membrane disruption and acetylcholinesterase inhibition, respectively. The present single dose study was designed to evaluate the toxicity and pharmacokinetics of orally administered potato glycoalkaloids (α-chaconine and α-solanine). It is the first published human volunteer study were pharmacokinetic data were obtained for more than 24 h post-dose. Subjects (2–3 per treatment) received one of the following six treatments: (1–3) solutions with total glycoalkaloid (TGA) doses of 0.30, 0.50 or 0.70 mg/kg body weight (BW), or (4–6) mashed potatoes with TGA doses of 0.95, 1.10 or 1.25 mg/kg BW. The mashed potatoes had a TGA concentration of nearly 200 mg/kg fresh weight (the presently recognised upper limit of safety). None of these treatments induced acute systemic effects. One subject who received the highest dose of TGA (1.25 mg/kg BW) became nauseous and started vomiting about 4 h post-dose, possibly due to local glycoalkaloid toxicity (although the dosis is lower than generally reported in the literature to cause gastro-intestinal disturbances). Most relevant, the clearance of glycoalkaloids usually takes more than 24 h, which implicates that the toxicants may accumulate in case of daily consumption.

Freezing by a Flat, Circular Surface Cryoprobe of a Tissue Phantom With an Embedded Cylindrical Heat Source Simulating a Blood Vessel

The effects of a thermally-significant blood vessel, simulated by an embedded acrylic tube, 4.8 mm outer diameter on the freezing field caused by a surface cryoprobe were studied experimentally in a tissue phantom. The flat, 15 mm diameter, circular cryoprobe was operated at a constant cooling rate of -8 degrees C/min by liquid nitrogen down to -60 degrees C. Water flow rates of 30 and 100 ml/min, at a constant temperature of 32.5 degrees C, were maintained in the embedded tube. The latter flow rate is typical to the lower range of blood flows in large arteries in the human body. The phase changing medium (PCM) used was a 30/70% by volume mashed potatoes flakes-water solution. Temperature measurements inside the PCM were performed in one plane perpendicular to the embedded tube, relative to which the cryoprobe was placed at 5 locations in separate experiments. This novel experimental method reduced the perturbation caused by the thermocouple junctions while facilitating rather detailed measurements of the temperature fields developing in the PCM. Results show the development of two hump-like formations on either side of the embedded tube. Freezing was retarded in the region away from the surface cryoprobe and under the tube. This accentuated the dominance of the axial effects, due to the embedded tube, over the radial ones due to the cryoprobe. Results of this study should be considered in designing protocols of cryosurgical procedures performed in the vicinity of thermally-significant blood vessels.

What Happens Next

What Happens Next Susan Jackson Rodgers (bio) The Man in the Garage A woman goes into her garage. She keeps an extra refrigerator there, for storing watermelons and party hors d'oeuvres. She is looking for a bag of frozen chicken that she knows she bought but cannot, now, an hour away from dinner, find. When she closes the refrigerator door (no chicken) she sees someone, a person, a man in fact, standing there, beside her husband's workbench. She is not frightened, and she understands, in the way you understand things in a dream, that the man is living there, in her garage. He is thirty-two (he says when she asks) but looks much younger. He has been using a sleeping bag that the woman recognizes as her son's. They store camping gear in the garage and the man has uncovered also a campstove and a canteen. She does not tell anyone about the man but instead begins to bring him food, the way you would feed a racoon or a stray cat living under your deck. When other people appear the man hides. Sometimes the woman thinks she is maybe imagining him. But each night when she comes out to the garage, smuggling food on paper plates, the man is there waiting for her, and smiles and thanks her and tells her it won't be long before he's back on his feet. The Analogy King He says, "It would be like leaving on a trip and forgetting your suitcase. It would be like if you loved mashed potatoes and all your wife ever served you was baked. It would be like driving a new car off the lot and having all four tires fall off at the first intersection. It would be like seeing your old man for the first time in twenty years and having him ask you, first thing, so how much money you making now? That's what it would be like." [End Page 136] Mango She sits with the baby in the kitchen, early morning. The baby bangs his drooly hands on the tray of the high chair. He vocalizes. He jabbers. He squeals. She is alone, she is here with the baby alone not just today but from the beginning and always. Last night, around one in the morning, a wild storm ripped a branch from the maple tree in the front yard, and the branch crashed on her roof. She lay awake and felt, really, that she didn't think she could do it. She honestly wasn't sure she could do it. Not just the limb on the roof but the water bill, the balancing of checkbooks and work schedules, the grocery shopping, the worrying over fevers over pink eye over ear infections over college entrance exams. But now, morning. She peels a mango. She is tired but not as tired as she thought she might be. The sun shines into brown puddles and bright leaves. The mango is slippery in her hands like a cool organ, and she almost drops it. The juice drips down fingers, wrists, forearms. She cuts the fruit. She sucks the large flat white pit, stringy mango between her teeth. She gives the baby a piece. He gums it, eyes wide at this new thing, hands already reaching for more. She gives him more. Fish House A couple goes to look at a house in the country. The realtor assures them it is perfect, it is just what they've been waiting for, their search is over, and will they please ignore the fish. When they get there they see what she means. Everywhere in and outside of the house there are fish. Goldfish, guppies, minnows. Plastic trash cans fill the yard, a dozen of them, water to the top, and if the couple looks closely they can see fish swimming deeply in the brackish water. The basement is crammed with tanks, tanks on every available surface, lined up on the floor, on tables, on shelves built specially for the tanks, the gurgling of the filters like waterfalls, like rapids, like static. Objects have been dropped into the tanks for effect: a...

Mathematical analysis of microwave heating process

The use of microwaves in the food industry is attributed to the lower time needed to increase the temperature of foodstuffs compared to the traditional heating methods. However, the heating is not uniform and the products show hot and cold spots. In order to analyze the behavior of microwaved foods a mathematical method was developed solving the unsteady state heat transfer differential equations. The model was applied to large systems for which Lambert’s law is valid because it leads to similar results as Maxwell equation. It takes into account variable thermal and electromagnetic properties. The numerical solution was developed using an implicit finite difference method in one dimensional systems (sphere, infinite cylinder and slab) and an alterning direction method in two- and three-dimensional conditions (finite cylinders and brick shaped products). It allows to predict temperature profiles and heating times. The model was validated with own data of mashed potato and meat products and with experimental data from literature obtained with agar gel, sodium alginate gel and whole potato.

Microbial Safety in Radio‐frequency Processing of Packaged Foods

ABSTRACT: Thermal resistance of Clostridium sporogenes (PA 3679) was determined at 115.6 °C, 118.3 °C, and 121.1 °C (240 °F, 245 °F, and 250 °F, respectively) in phosphate buffer (pH 7.0) and mashed potatoes (pH 6.3) using aluminum thermal‐death‐time (TDT) tubes developed at Washington State Univ. D‐values were 1.8, 1.1, and 0.62 min in phosphate buffer and 2.2, 1.1, and 0.61 min in mashed potatoes at 115.6 °C, 118.3 °C, and 121.1 °C, respectively. Z‐values were 12 °C and 10 °C in phosphate buffer and mashed potatoes, respectively. The thermal inactivation kinetic results were then used to validate a novel thermal process based on 27.12 MHz radio frequency (RF) energy. Trays of mashed potatoes inoculated with PA 3679 were subjected to 3 processing levels: target process (F0∼4.3), under‐target process (F0∼2.4), and over‐target process (F0∼7.3). The microbial challenge test data showed that microbial destruction from the RF process agreed with the calculated sterilization values. This study suggests that thermal processes based on RF energy can produce safe and shelf‐stable packaged foods.

BEHAVIOR OF STREPTOCOCCUS PYOGENES IN MASHED POTATOES

ABSTRACTStreptococcus pyogenes is widely recognized as a human pathogen. Whereas person‐to‐person transmission is the most common transmission mechanism for this pathogen, some outbreaks of S. pyogenes disease have been reported to occur in association with consumption of contaminated foods such as shrimp or potato salads. In this study, the behavior of S. pyogenes was studied in mashed potatoes as a function of storage temperature, types and amount of background biota and type of ingredients. Combined mashed potatoes (potatoes, butter, milk, egg and table salt) or plain mashed potatoes (potatoes only) were inoculated with a 5‐strain cocktail of S. pyogenes and stored at 7, 25, 35 or 37C. At intervals during storage, samples were collected for counting S. pyogenes in blood agar plates or blood agar added with sodium azide, polymyxin and crystal violet. Mashed potatoes obtained from fast‐food restaurants were used to determine the fate of S. pyogenes as affected by changes in aerobic mesophiles, coliform and lactic acid bacteria counts. S. pyogenes was able to survive in mashed potatoes stored at 7C and to grow in mashed potatoes stored at 25 or 37C with lag phase lengths of 3 and 2 h and generation times of 26.0 and 25.3 min, respectively. The generation time of S. pyogenes in plain mashed potatoes was 30.7 min at 35 C. Presence of active background biota at 2–3 log10 CFU/g concentrations did not prevent growth of S. pyogenes when stored at 35C. These results contribute to a better understanding of the potential for S. pyogenes to cause foodborne outbreaks.