Quality changes of pork during frozen storage: comparison of immersion solution freezing and air blast freezing

This study evaluated the effects of freezing method and storage time on the quality changes of pork longissimus thoracis (LT). The results showed that, compared to air blast freezing (AF), better microstructure was observed in pork under immersion solution freezing (ISF) mainly due to higher freezing rate. ISF group had significantly lower thawing loss at 1, 31 and 91 days and higher shear force at 1 day than AF (P < 0.05). A significant reduction in TBARS value at 61 and 91 days was observed in ISF samples (P < 0.05). No significant differences were observed between the two treatments in the colour, cooking loss and sulfhydryl groups (P > 0.05). All quality indicators were significantly affected by storage time (P < 0.05). It is concluded that ISF could maintain better microstructure, improve water-holding capacity and inhibit lipid oxidation during pork LT frozen storage.     

Frozen storage characteristics of low-salt and low-fat beef patties as affected by Wakame addition and replacing pork backfat with olive oil-in-water emulsion

Characteristics of beef patties with low-salt (0.5%) and low-fat (<10%) contents were studied during frozen storage as affected by addition of Wakame seaweed (3%) and partial or total replacement of pork backfat with olive oil-in-water emulsion. Patties with Wakame presented less (P < 0.05) thawing and cooking losses and were softer (P < 0.05) than patties without seaweed. A softening effect (P < 0.05) induced by olive oil emulsion was observed only in seaweed-free patties. Lipid oxidation and microbiological counts in reformulated products were not a limiting factor for frozen stability. Wakame incorporation increased (P < 0.05) mineral contents, but all products presented the same Na/K ratio. Observed changes in microstructure were associated with seaweed addition (formation of alginate chains). All products were judged acceptable by the sensory panel. In the course of frozen storage no important changes were found in the target properties due to the different treatments.     

Fate of Listeria monocytogenes during freezing,thawing and home storage of frankfurters

Little information is available regarding the fate of Listeria monocytogenes during freezing, thawing and home storage of frankfurters even though recent surveys show that consumers regularly store unopened packages in home freezers. This study examined the effects of antimicrobials, refrigerated storage, freezing, thawing method, and post-thawing storage (7 °C) on L. monocytogenes on frankfurters. Inoculated (2.1 log CFU/cm²) frankfurters formulated without (control) or with antimicrobials (1.5% potassium lactate plus 0.1% sodium diacetate) were vacuum-packaged, stored at 4 °C for 6 or 30 d and then frozen (−15 °C) for 10, 30, or 50 d. Packages were thawed under refrigeration (7 °C, 24 h), on a countertop (23 ± 2 °C, 8 h), or in a microwave oven (2450 MHz, 1100 watts, 220 s followed by 120 s holding), and then stored aerobically (7 °C) for 14 d. Bacterial populations were enumerated on PALCAM agar and tryptic soy agar plus 0.6% yeast extract. Antimicrobials completely inhibited (p < 0.05) growth of L. monocytogenes at 4 °C for 30 d under vacuum-packaged conditions, and during post-thawing aerobic storage at 7 °C for 14 d. Different intervals between inoculation and freezing (6 or 30 d) resulted in different pathogen levels on control frankfurters (2.1 or 3.9 log CFU/cm², respectively), while freezing reduced counts by <1.0 log CFU/cm². Thawing treatments had little effect on L. monocytogenes populations (<0.5 log CFU/cm²), and post-thawing fate of L. monocytogenes was not influenced by freezing or by thawing method. Pathogen counts on control samples increased by 1.5 log CFU/cm² at d-7 of aerobic storage, and reached 5.6 log CFU/cm² at d-14. As indicated by these results, consumers should freeze frankfurters immediately after purchase, and discard frankfurters formulated without antimicrobials within 3 d of thawing and/or opening.     

Low-fat pork liver pâtés enriched with n-3 PUFA/konjac gel: dynamic rheological properties and technological behaviour during chill storage

Low-fat pork liver patés enriched with n-3 PUFA/konjac gel were formulated by replacing (total or partially) pork backfat by a combination of healthier oils (olive, linseed and fish oils) and konjac gel. Dynamic rheological properties and technological behaviour of patés during chill storage (2 °C, 85 days) were analysed. Cooking yields were affected (P<0.05) by formulation, with percentages ranging between 88 and 98%. According to the frequency sweep test, patés presented a gel/emulsion-like pattern with a loosely-structured network and the consistency of a viscoelastic gel. Thermal processing caused the formation of a protein gel network with a considerable element of emulsion-like characteristics. Patés became lighter and less red (P<0.05) during chill storage. Purge losses of around 1% were observed at the end of the storage period, irrespective of formulation. Textural parameters of patés were affected by formulation and storage time. The results suggest that the replacement of pork back fat by oil-in-water emulsion and the incorporation of konjac gel could provide a mixture of ingredients that effectively mimics the normal animal fat content in patés.     

Technological and sensory characteristics of reduced/low-fat,low-salt frankfurters as affected by the addition of konjac and seaweed

This paper reports the effect of an edible seaweed, Sea Spaghetti (Himanthalia elongata), on the physicochemical (emulsion stability, cooking loss, colour, texture, residual nitrite and microstructure) and sensory characteristics of reduced- and low-fat, low-salt (NaCl) frankfurters prepared with konjac gel as a fat substitute. The effects on emulsion stability of substituting konjac gel for pork backfat were conditioned by the proportion of the substitution. Incorporation of a combination of Sea Spaghetti/konjac gel (accompanied by reduction in salt) increased (P < 0.05) cooking loss and reduced (P < 0.05) emulsion stability in the gel/emulsion systems. Incorporation of Sea Spaghetti/konjac gel produced a decrease (P < 0.05) of lightness (L∗) and redness (a∗) values and an increase (P < 0.05) of yellowness (b∗) as compared to the other samples. The effect of adding seaweed on the texture parameters of low-salt frankfurters varied depending on the proportion of konjac gel used in the formulation. Morphological differences in frankfurter microstructure were observed as fat content was reduced and konjac gel increased. Incorporation of a combination of Sea Spaghetti/konjac gel caused the formation of a more heterogeneous structure, in which the seaweed was integrated in the meat protein matrix.     

Antioxidant activity of Carob fruit extracts in cooked pork meat systems during chilled and frozen storage

The purpose of this study was to evaluate the effect of adding condensed tannins in the form of non-purified (Liposterine^®) or purified (Exxenterol^®) extracts obtained from Carob fruit to prevent lipid cooked pork meat systems from oxidising during chilling and frozen storage. The antioxidant activity of these extracts was compared with that of α-tocopherol. Meat lipid alteration was evaluated as thiobarbituric acid reactive substances content (TBARS) and polar material-related triglyceride compounds followed by high-performance size-exclusion chromatography (HPSEC). TBARS levels were lower (P < 0.05) in samples containing Liposterine (LM), Exxenterol (EM), and α-tocopherol (TM) than in control sample (CM) under chilled storage. TBARS formation was similar (P > 0.05) for LM and EM but lower (P < 0.05) than for TM. Polar material increased several times in all samples, but significantly less in TM and EM than in LM. Thermal oxidation compounds determined by HPSEC were lower (P < 0.05) in EM than in LM or TM. The changes in polar material were proportionally smaller after six months frozen storage than after chilled storage, with Exxenterol displaying the highest antioxidant protection. Therefore Carob fruit extracts can be successfully used to reduce fat alteration in cooked pork meat at chilled and frozen temperatures.     

Konjac gel fat analogue for use in meat products: Comparison with pork fats

The paper reports a study of the characteristics of konjac gel fat analogue as compared to types of pork fat for use in fat reduction strategies for meat products. Various characteristics—colour, mechanical/rheological behaviour and thermal properties—of pork fats (backfat-PBF and trimmed fat-PTF) and konjac gel (KFG) with different physical structures (intact or ground to 4 and 8 mm) were studied. Pork fat melting processes were evaluated by differential scanning calorimetry (DSC) at above- and below-zero temperature ranges with PBF and PTF always showing similar net results. KFG did not show any thermal event in the range from −40 to 100 °C except the freezing/melting of its constitutional water. While water and fat binding properties of pork fats were affected by fat type and structural disintegration (ranging between 0 and 77%), in all cases KFG presented excellent thermal water binding (<1%). As compared to KFG, PBF showed greater (P < 0.05) hardness, chewiness, penetration force, gel strength, extrusion force and work of extrusion. These differences were minimized after grinding. Kramer shear values in KFG were greater (P < 0.05) than in PBF when this was ground to 4 mm, but lower (P < 0.05) at 8 mm. The highest Kramer shear values (P < 0.05) were recorded in PTF irrespective of the degree of disintegration. Rheological analyses indicate that the behaviour of KFG, which is thermally stable, is predominantly elastic during heating and exhibits rheological thermal behaviour (at over 40 °C) similar to that of pork backfat.     

Postharvest quality and shelf life of radish microgreens as impacted by storage temperature,packaging film,and chlorine wash treatment

Microgreens are new and emerging products, which are young seedlings of vegetables and herbs. A recent study showed that microgreens contain higher nutrients compared to their mature counterparts. However, they typically have a short shelf life (1–2 days) at ambient temperature. The objective of this study was to optimize postharvest handling conditions to reduce the quality loss and extend the shelf life of daikon radish (Raphanus sativus L. var. longipinnatus) microgreens. Storage temperature, packaging film, and wash treatment were investigated. Changes in headspace composition, quality index, chlorophyll concentration, tissue electrolyte leakage, and aerobic mesophilic bacteria (AMB) and yeast & mold (Y&M) counts were monitored periodically during storage. Results indicated that (1) storage temperature significantly (P < 0.05) affected package atmosphere, product quality and shelf life. One degree Celsius was the optimal temperature for storage of radish microgreens with no chilling injury observed; (2) film oxygen transmission rate (OTR) significantly (P < 0.05) affected O₂ and CO₂ composition, but OTR did not significantly affect quality attributes during 28 days of storage at 1 °C; (3) Chlorine wash treatment (100 mg/L) significantly reduced initial microbial populations by 0.5 log cfu g⁻¹, including AMB and Y& M. However, microbial populations rebounded after day 7.     

Chemical and biochemical changes of hybrid catfish fillet stored at 4 °C and its gel properties

Chemical and biochemical changes of aquacultured hybrid catfish fillet (Clarias macrocephalus × Clarias gariepinus) and its gel-forming ability as affected by age and sex of fish along with storage time were investigated. Fillets were stored at 4 °C for 0, 3, 6, 9, 12 and 15 days. There was no significant effect of sex and age of fish as well as storage time on fat, moisture and ash contents (P > 0.05). The total protein, water soluble protein, and salt soluble protein contents of the fillets significantly decreased with storage time (P < 0.05). On the other hand, pH, total volatile base nitrogen (TVB-N) and autolytic degradation products (ADP) increased as storage time continued (P < 0.05). Decreases in Ca²⁺-ATPase activity and gel properties were observed as storage time increased. However, there was no significant effect of either sex or age of fish on textural properties of gel (P > 0.05). Hybrid catfish fillet stored at 4 °C should be processed within 6 days.     

Effect of sub‐freezing storage (−6, −9 and −12 °C) on quality and shelf life of beef

Based on the results of low field nuclear magnetic resonance (LF‐NMR) in our current study (the frozen state of ?6, ?9 and ?12 °C were nearly the same with extremely low free water content), ?6, ?9 and ?12 °C was designated as sub‐freezing temperatures. The effects of sub‐freezing storage compared with conventional chilling (4 °C), superchilling (?1 °C) and conventional freezing (?18 °C) on the quality and shelf life of beef were analysed. Results showed that the shelf life of beef is extended to 84 and 126 day at ?6 °C and ?9 °C, respectively. However, the TVB‐N values of the samples stored at ?12 °C and ?18 °C remained below 15 mg/100 g even on 168 day. Furthermore, shear force, colour, pH, thiobarbituric acid reactive substances (TBARS) and sensory properties were also measured. Consequently, the sub‐freezing storage has significantly extended the shelf life of beef compared to chilling and superchilling (P < 0.05). Moreover, no significant difference (P > 0.05) was found between the indicators for quality and shelf life of samples stored at ?12 and ?18 °C throughout 168 days.     

Effect of preformed konjac gels,with and without olive oil,on the technological attributes and storage stability of merguez sausage

In order to improve the fat content of fresh sausages (merguez), the effects of both reducing beef fat level (by konjac gel-KG) and incorporing olive oil (in a konjac matrix-OKM) on nutritional, quality characteristic and refrigerated storage stability were studied. Fat reductions in merguez sausages of between 53 and 76% were achieved when beef fat was replaced with KG; the proportion reached 34–49% using OKM as a beef fat replacer, where 23 to 36% of total fat in the merguez was from olive oil. The merguez contained substantial amounts of some minerals (Mg and Fe). Sensory analysis revealed no significant differences between the control and the reformulated products, which had relatively low levels of lipid oxidation. Shelf life and biogenic amines of merguez sausage were not affected by formulation during refrigerated storage. Therefore, the use of konjac materials as fat replacers could reduce total caloric energy by replacing/reducing beef fat and improving sausage formulation to achieve healthier merguez products.     

Influence of blanching and low temperature preservation strategies on antioxidant activity and phytochemical content of carrots, green beans and broccoli

The objective of this study was to investigate the effect of blast freezing and blanching in combination followed by chilling, on the antioxidant activity (ARP), phenols, ascorbic acid and colour of broccoli, carrots and green beans. No significant changes (p > 0.05) in ARP of blanched frozen (BLFR) broccoli, carrot and green beans were observed. In contrast, UBFR (unblanched frozen) treatments caused a significant decrease (p < 0.05) in ARP and ascorbic acid content of vegetable samples. BLFR treated samples had better retention of antioxidant activity and ascorbic acid as compared to UBLR counterparts at chill storage (4 °C) for 7 days. However, no significant changes were observed in phenol content for all vegetables. Ascorbic acid decreased exponentially for both blanched and unblanched samples. The reaction rate constant (k) increased from 1.06 × 10⁻¹ day⁻¹ to 1.17 × 10⁻¹ day⁻¹ for blanched and unblanched broccoli florets and from 4.6 × 10⁻³ day⁻¹ to 1.98 × 10⁻¹ day⁻¹ for blanched and unblanched carrots during 7 days storage. Result presented here indicates greater stability of nutritional parameters for BLFR samples compared to UBFR samples during 7 days storage at 4 °C for all vegetables.     

Survival of Lactobacillus delbrueckii UFV H2b20 in ice cream produced with different fat levels and after submission to stress acid and bile salts

The survival of Lactobacillus delbrueckii UFV H2b20 in three ice cream formulations (low fat, fat free and high fat) was evaluated after the processing and storage at ?16 °C. The survival of L. delbrueckii UFV H2b20 was not significantly affected (P > 0.05) in three ice cream formulations after processing. The same result was observed during storage for 40 days at ?16 °C. Cells of L. delbrueckii UFV H2b20 incorporated in three ice cream formulation survived when exposed to acid stress and bile salts. The results demonstrate that L. delbrueckii UFV H2b20 has potential for being used in ice cream and capacity to resist acid stress and to grow in the presence of bile salts. This demonstrates that reduction of fat in ice cream does not compromise the viability of L. delbrueckii UFV H2B20.     

Influence of different thawing methods on physicochemical changes and protein oxidation of porcine longissimus muscle

The objective of the present study was to elucidate the physicochemical changes and protein oxidation of porcine longissimus muscle as influenced by different thawing methods. Five kinds of thawing methods, comprising of refrigerator thawing (RT, 4 °C), ambient temperature thawing (AT, 20 °C), water immersion thawing (WT, 14 °C), lotic water thawing (LT, 9 °C), and microwave thawing (MT), were used. There were significant effects on the porcine meat quality due to different thawing methods. RT had the least quality loss and the physicochemical characteristics of pork were closer to fresh muscle than the other thawing methods. MT significantly increased thawing loss, cooking loss, cutting force, carbonyl content, and TBARS (thiobarbituric acid-reactive substances) value, but decreased a* value and Ca-, K-ATPase activities (P < 0.05). Microstructural changes in experimental muscle showed that MT induced visibly larger gap between muscle fibers and tore more muscle fiber bundles compared to the other thawing methods. The reduction of Ca- and K-ATPase activities (P < 0.05) of myofibrillar protein was consistent with the increases in carbonyl content and TBARS value (P < 0.05). The results demonstrated all the thawing methods could cause porcine lipid and protein oxidation. Gel electrophoresis patterns of porcine muscle displayed that different thawing methods did not induce obvious protein aggregates and fragments.     

Characterization of Siahmazgi cheese,an Iranian ewe's milk variety: Assessment of physico-chemical,textural and rheological specifications during ripening

Siahmazgi cheese is an Iranian locally-made cheese produced from ewe's milk or a mixture of ewe and goat's milks in the suburbs of Rasht in the north of Iran. This kind of cheese is kept in sheepskin for six months under special condition which cause distinct physicochemical and textural characteristics. Therefore, in the present study the effect of ripening time (6 months) on the chemical, physicochemical, rheological and textural characteristics of Siahmazgi cheese (18 samples) was investigated. The rheological and textural properties were determined using rheometer (frequency sweep) and texture analyzer (uniaxial compression). Based on our findings, the measured values including pH, titratable acidity (TA), dry matter, fat, protein, ash, salt content, water soluble nitrogen in total nitrogen, and non-protein-nitrogen in total nitrogen significantly increased during ripening (P < 0.05). Furthermore, the results showed that the six-month ripened Siahmazgi cheese contained high values of dry matter (59.95 ± 0.08 g/100 g), salt (5.65 ± 0.05 g/100 g), and ash (7.24 ± 0.02 g/100 g). Regarding rheological and textural properties, storage modulus (G′), loss modulus (G″), fracture stress (σ_f) and firmness increased while loss tangent and fracture strain decreased.     

Evaluation of fish meat noodles: physical property,dough rheology,chemistry and water distribution properties

The present study reports the rheological, textural, structural and water distribution properties of fish meat noodles. The results showed that storage and loss modulus were increased when 20% fish meat was added while decreased with the addition of >20% fish meat, whereas loss rate behaved vice versa. The moisture and fat content increased significantly (P < 0.05) while water absorption index was decreased upon the increment of fish meat compared to control. Lightness of dough and hardness of noodles decreased significantly (P < 0.05) while redness and yellowness were increased. Similarly, less swelled starch granules and dominancy of protein network over starch granules were observed in microstructure. The amount of free water was increased while bound water was decreased when >20% fish meat was added during low-field nuclear magnetic resonance. The findings suggest the feasibility of adding 15–20% fish meat for the proper structure and chemistry of noodles.     

Characteristics and application of enzyme-modified carboxymethyl starch in sausages

Enzyme-modified carboxymethyl starch (ECMS) was prepared by etherification of starch and enzymatic hydrolysis. The characteristics of ECMS and its application as fat replacers in 10 g/100g and 20 g/100 g target fat sausages were evaluated. FT-IR spectroscopy indicated that the absorption peaks of carboxyl in ECMS were characterized at 1635 and 1426 cm⁻¹. ECMS had better paste clarity and freeze–thaw stability than enzyme-modified starch (ES) or native starch. The addition of ECMS in sausages increased (P < 0.05) water holding capacity and emulsion stability of the products. Sensory analysis showed that the 10 g/100 g fat sausage with added ECMS was similar (P > 0.05) to the 20 g/100 g fat sausage control for juiciness, oiliness, texture, flavour and overall acceptability at storage days of 0, 7, 14 and 21. The results indicated that the new multiplex modified starch-ECMS could be used as a suitable fat replacer since it offset some of the changes led by fat reduction.     

Effects of somatic cell counts in milk on physical and chemical characteristics of yoghurt

The quality of plain stirred yoghurt produced from whole milk with somatic cell counts (SCC) at low (147,000 cells mL⁻¹), intermediate (434,000 cells mL⁻¹) and high (1,943,000 cells mL⁻¹) levels was examined. Each milk treatment was obtained from selected cows, according to its SCC status and milk composition. Yoghurt samples were analysed on days 1, 10, 20 and 30 after production. Analyses included pH, acidity, fat, lipolysis (expressed as free fatty acids, FFA), proteolysis and apparent viscosity. Viscosity of high SCC yoghurt was higher (P<0.05) than the low SCC yoghurt on days 10, 20 and 30 of storage. High SCC yoghurt also had higher FFA content (P<0.05). SCC did not affect pH, acidity, fat content and proteolysis of the yoghurt (P>0.05). Results indicate that SCC in milk increases the lipolysis in the resulting yoghurt during storage for 30 d.     

Impact of extended refrigerated storage and freezing/thawing storage combination on physicochemical and microstructural characteristics of raw whole and skimmed sheep milk

The impact of freezing (1 month + thawing at 7 or 25 °C) and extended refrigeration (4 days, 7 °C) on physicochemical and microstructural characteristics of raw whole and skimmed sheep milk were assessed. Refrigerated storage resulted in higher sedimentation and creaming (whole milk), possibly due to proteases and agglutinins. Freezing/thawing processes in whole milk increased the particle size and creaming when samples were thawed at 7 °C. Skimmed milk showed an increase in buffering capacity and a reduction in soluble calcium immediately after thawing at 25 °C, suggesting that although the changes in fat are the main alterations caused by slow freezing of sheep milk, minor changes in saline balance can occur. An evaluation of the results showed that frozen and thawed milk in domestic equipment (commonly found in smallholdings) alter the milk microstructure, and it is therefore preferable to use extended refrigeration to accumulate the milk before dairy production.     

Physicochemical and rheological properties of purees based on Mafafa (Xanthosoma robustum) and quinoa (Chenopodium quinoa Willd.) with the addition of cryoprotectants

Growing interest in processed frozen products with similar characteristics to natural products has generated the study of new products in the food industry field. The characteristics of each matrix, the process of elaboration, composition, and structure of the additives and the interactions amongst these modify the food's texture, structure, physical and sensory properties and, hence, interfere directly with consumer acceptance. This research studied the effect of adding cryoprotectors during frozen storage on the rheological, physicochemical, structural, and microbiological properties in a Mafafa‐quinoa‐olive oil puree. To carry out the study, the rheological properties were determined through dynamic oscillatory tests and in steady state; likewise, the physicochemical properties (humidity, color, pH, and syneresis) were analyzed. Regarding physicochemical properties, the humidity content in the purees formulated varied between 57 and 74%, without important variation (p > .05) with respect to the formulation, however, in the storage during the freezing/thawing process, this parameter diminished in greater proportion in those purees containing carrageenan as cryoconservant. Both the addition of cryoconservants and the storage time affected significantly (p < .05) the puree's syneresis, with the degree of exudation being lower in the formulation containing xanthan gum at 1% w/w. During the freezing/thawing process, decreased apparent viscosity was noted. Additionally, the analysis of the viscoelastic properties of the purees evidences that already described, given that a significant effect (p < .05) was observed of the formulation of purees in the elastic component G′, in contrast with a notable decrease in the viscous component G″.