Optimizing Sensorial Quality of Iranian White Brine Cheese Using Response Surface Methodology

ABSTRACT: Response surface methodology was used to evaluate the effects of processing variables, such as ripening time (20 to 60 d), ripening temperature (6 to 10°C), level of rennet added (1 to 2 g/100 kg milk), and brine concentration (8% to 14%, w/v), on the sensorial quality of Iranian pickled cheese (feta type). Optimization of sensorial quality was performed by canonical analysis to derive the stationary point. Based on contour plots and canonical analysis, optimum conditions were ripening time 32 d, ripening temperature 8.3°C, level of rennet added 1.6 g/100 kg of milk, and brine concentration 11%. Predicted sensory score was 20.76 from maximum score of 25.     

Effect of artisanal kid rennet paste on lipolysis in semi-hard goat cheese

This study examined the use of hygienised kid rennet pastes in model cheese systems and also in goat milk semi-hard cheeses to promote lipolysis. The results obtained indicated that the use of rennet paste caused greater lipolysis and increased, mostly, the short-chain free fatty acid (FFA) content. The model systems made with whole goat’s milk using rennet paste and commercial rennet mixture exhibited a higher FFA content than did the rennet paste-free controls (31,600 vs. 25,600 μmol/kg cheese). For the pilot cheeses made with bovine rennet and rennet paste mixture, the increase in FFA level after 45 days of ripening compared with the cheeses prepared only with commercial rennet was as much as 6600 (μmol/kg cheese) and the increase in the butyric acid content was also 1650 (μmol/kg cheese). Moreover, after 15 days of ripening, industrially prepared cheeses made with rennet paste exhibited greater levels of FFA than did the cheeses made with commercial rennet (11,500 μmol/kg at 45 days of ripening). Their flavour was stronger and the organoleptic characteristics were better accepted, which implies less ripening time for commercial cheese manufacture.     

Biogenic amines in Iranian white brine cheese: modelling and optimisation of processing factors

The simultaneous effects of processing factors such as ripening time (25–75 days), ripening temperature (4–14 °C) and brine concentration (10–13%) on biogenic amines content, proteolysis and sensory score of Iranian white brine cheese were studied, in 12 cheeses. Response surface methodology (RSM) was used to minimise biogenic amines content. At low level of ripening time, biogenic amines content decreased with increasing levels of brine concentration but at high level of ripening time, brine concentration had inverse effect. Ripening time showed quadratic effect on biogenic amines content. Based on biogenic amines content and sensory score, the optimum conditions were 13% brine and ripening at 9–14 °C for 43–65 days.     

Phase structures impact the rheological properties of rennet-casein-based imitation cheese containing starch

The dynamic rheological and microstructural properties of rennet-casein-based imitation cheeses containing various concentrations of potato starch were investigated using a stress-controlled rheometer and confocal laser scanning microscopy. The influence of added starch on the size of the oil droplets in the imitation cheeses was also examined. Imitation cheeses with 0–15% protein replaced by starch were processed in a Rapid Visco Analyser (RVA) at 90 °C for 10 min at a shear rate of 800 rev/min and were then evaluated using oscillatory shear measurement and a temperature sweep (20–90 °C). The storage modulus (G′) of the rennet casein imitation cheeses increased abruptly at added starch concentrations >4%. In the temperature range 20–90 °C, tan δ of the imitation cheeses decreased with increasing starch concentration and was <1 at added starch concentrations >4%. A binary continuous phase consisting of a protein phase and a starch phase was observed in systems containing >4% starch, whereas the starch was dispersed in the protein matrix as small particles of irregular shapes at added starch concentrations ≤4%. As the dispersed phase, the size of the oil droplets increased with starch addition in the imitation cheeses. The marked increase in G′ and the reduction in tan δ may be attributed to the formation of a binary continuous separated phase structure in imitation cheeses containing added starch that is driven by thermodynamic incompatibility between rennet casein and starch.     

The evolution of free fatty acids during the ripening of Idiazábal cheese: influence of rennet type

 The object of the present study was to determine the influence of the rennet type on the free fatty acid (FFA) content of Idiazábal cheese. Varying this parameter during cheese-making resulted in significant differences in FFA content in the cheeses during ripening. The main FFAs in both cheese batches were caproic acid (C6 : 0) and capric acid (C10 : 0). The differences between the extreme values for the lipolysis rate were around 45%, which emphasizes the importance of the cheese-making procedure employed on lipolysis in this type of cheese. The use of locally made rennet in the preparation of Idiazábal cheese increased the level of lipolysis in the cheese. Received: 4 December 1998 / Revised version: 18 March 1999     

Modeling and optimization of lipase-catalyzed synthesis of phytosteryl esters of oleic acid by response surface methodology

Enzymatic esterification of phytosterols with oleic acid to produce phytosteryl esters was performed in hexane. Response surface methodology was used to model the reaction. Candida rugosa lipase was the biocatalyst for the reaction. The reaction factors investigated were temperature (Te = 35–55 °C), reaction time (t = 4–24 h), substrate molar ratio (Sr = 1–3, oleic acid:phytosterols), and enzyme amount (En = 2–10%). Well-fitting quadratic polynomial regression model for degree of esterification (DE) was established after regression analysis with backward elimination and verified by a χ² test. All factors investigated positively affected DE, with t having the greatest effect followed by En, Sr, and Te. The quadratic terms of t, Sr, and En showed negative effects on DE, whereas, that of Te had no effect on DE. Optimal reaction conditions were: Te, 51.3 °C; t, 17.0 h; Sr, 2.1; En, 7.2% and DE was 97.0 mol% under these conditions.     

Identification of volatile compounds in soymilk using solid-phase microextraction-gas chromatography

Headspace solid-phase microextraction (HS-SPME) gas chromatography was used to analyze volatile compounds in soymilk. The effect of incubation temperature (30–70 °C) and time (5–60 min), sample volume (0.5–5 ml), and type of SPME fiber (65 μm CWAX–DVB, 70 μm PDMS–DVB and 85 μm CAR–PDMS) were studied. All the factors markedly affected sensitivity and selectivity. Among the three fibers tested, the CAR–PDMS fiber had greater sensitivity to a more diverse range of volatile compounds, followed by PDMS–DVB and CWAX–DVB fibers using both soymilk and water with added volatiles as a matrix. SPME optimization conducted using a water matrix with added known soy volatiles, showed the following conditions to be optimal for selectivity and sensitivity: incubation temperature of 40 °C, incubation time of 20 min, and sample volume of 5 ml (for volatile compound concentration of ∼25 ppm). The selected conditions were used for the analysis of volatiles in six commercial soymilk samples. A total of 30 volatile compounds were identified. The results showed significant differences in the total volatiles of the soymilk products. The repeatability of measurements of total volatiles compounds of soymilk was ∼5.4% for four replicate analyses. Similar volatile compounds were present in all the samples analyzed but at different concentrations. The method proposed is simple and can be used to measure both hexanal and/or total volatiles in soymilk samples.     

Lamb rennet paste in ovine cheese manufacture. Lipolysis and flavour

In a preliminary study with commercial ewe's milk cheeses, there were statistically significant differences in the sensory evaluation scores and the amounts of short-chain (C4–C10) free fatty acids (FFAs) between cheeses made with lamb rennet paste or bovine rennet. Experimental ewe's milk cheeses were manufactured with 2 levels of artisanally produced lamb rennet paste and 2 levels of bovine rennet in 50 L vats, with a manufacturing replicate done within 1 week. Total coagulating activity was 2500 RU for cheeses manufactured with a high amount of rennet or 1000 RU for cheeses manufactured with a low amount of rennet. The two batches of lamb rennet pastes used had 4.0 (early Spring) and 6.5 U g⁻¹ lipase (late Spring), whereas no lipase activity was detected in bovine rennets. The total concentration of FFAs in cheeses manufactured with lamb rennet paste was significantly higher than in cheeses manufactured with bovine rennet, regardless of ripening time and time of the year. Lipolysis in the former cheeses increased with the total units of lipolytic activity added. The increase in lipolysis in cheeses made with lamb rennet was primarily due to higher amounts of short-chain fatty acids (C4–C10). Butyric acid was the main FFA in cheeses made with lamb rennet paste, representing 34.5 μmol 100 μmol⁻¹ (low level of rennet) and 44.2 μmol 100 μmol⁻¹ (high level of rennet) of the total FFAs, whereas it represented only 17 μmol 100 μmol⁻¹ of the total FFAs in all cheeses made with bovine rennet. The concentration of individual FFAs of chain length <C12 were significantly higher in cheeses made with lamb rennet paste than in cheeses made with bovine rennet. Cheeses made with lamb rennet paste received significantly higher intensity scores for odour and flavour intensity, sharp odour, ‘piquant’ and bitter flavours and ‘natural rennet’ odour and flavour.     

Development of a solid phase microextraction protocol for the GC–MS determination of volatile off-flavour compounds from citral degradation in oil-in-water emulsions

The conditions for headspace solid phase microextraction (HS-SPME) analysis of volatile off-flavour compounds in citral emulsion were determined. Type of SPME phase (65 μm PDMS/DVB, 100 μm PDMS and 75 μm CAR/PDMS), adsorption temperature and salt concentration were significant factors affecting total peak area in the gas chromatogram and optimised in one factor experiments. Then, adsorption temperature (30–50 °C), adsorption time (20–40 min), and salt concentration (0–6 M) were studied to develop HS-SPME condition for obtaining the highest extraction efficiency. PDMS/DVB in 65 μm was the optimum fiber because of high adsorption efficiency and good reproducibility. The optimal condition was adsorption at 50 °C for 40 min and 6 M salt added to sample. Good Linearity, high recovery, good reproducibility and low limit of detection (LOD) for all off-odour compounds according to the optimised SPME conditions indicated that the SPME procedure was applicable for the analysis of the degraded citral products in headspace volatile of emulsion.     

Rennet coagulation of sheep milk processed by ultrafiltration at low concentration factors

The ultrafiltration (UF) of sheep milk is carried out in concentration mode in order to evaluate the variation of the rennet clotting properties of the concentrates as a function of the volumetric concentration factors up to a value of 2.0. The UF unit is equipped with 25.5 cm² of membrane surface area. The cellulose acetate laboratory – made membrane has a molecular weight cut-off of 7000 Da. The evolution pattern of the rennet clotting properties of the skimmed sheep milk feed and UF retentates was assessed by the Optigraph. A significant increase on curd firmness and rate of curd firming was detected with the increase of the protein concentration, while RCT show a tendency to increase with milk protein content. The variation of curd firmness and rate of curd firming with the protein concentration was linear and correlations were established.     

The effects of ripening period,nitrite level and heat treatment on biogenic amine formation of “sucuk” – A Turkish dry fermented sausage

The effects of ripening period (1–13 days), nitrite level (45–195 ppm) and heat treatment (30–90 °C) on biogenic amine formation of sucuk were investigated using the central composite rotatable design of response surface methodology.     

The effects of high salt and low pH on the water-holding of meat

The study investigated the water-holding (WH) in meat in the pH–NaCl (ionic strength) combinations that prevail in dry sausages during fermentation and drying. WH in raw beef homogenates, with 230% added water, was determined by centrifugation at pH values of 5.47–4.60, and ionic strengths (μ) 0.50–1.50. The minimum WH in relation to pH was at pH 4.8, but at higher pH values, the WH optimum was at 1.0–1.5 μ; at lower pH-values (< 5.0) the optimum was more pronounced at 1.0 μ. The WH reducing effect by pH decrease was stronger than the effect of μ. At lower pH values, the relative effect of μ on WH was higher compared to that of pH than at higher pH values. The pH–salt combinations prevailing in fermented sausage in the beginning of the ripening produced a high WH, which decreased, first with pH decrease and then in the last period of ripening mainly due to the increase of ionic strength.     

Vitamin (B1, B2, B3 and B6) content and oxidative stability of Gastrocnemius muscle from dry-cured hams elaborated with different nitrifying salt contents and by two ageing times

The effect of the amount of added nitrate and nitrate plus nitrite to dry-cured hams on the vitamin (B1, B2, B3, B6) content, the antioxidant enzyme superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSHPx) activities and the thiobarbituric acid reactive substances (TBARS) was assessed in Gastrocnemius muscle at the end of two ripening processes. Five different curing mixtures (Hi–N: 600 KNO₃; Lo–N: 150 KNO₃; Hi–Mix: 600 KNO₃ + 600 NaNO₂; Lo–Mix: 150 KNO₃ + 150 NaNO₂; Hi–Mix/Asc: 600 KNO₃ + 600 NaNO₂ + 500 sodium ascorbate, expressed as mg of salts added on surface per kg of fresh ham) were evaluated in dry-cured hams aged for 11.5 months (standard process, SP) and 22 months (long process, LP).     

Lipolysis in cheddar cheese made from raw, thermized, and pasteurized milks

The evolution of free fatty acids (FFA) was monitored over 168 d of ripening in Cheddar cheeses manufactured from good quality raw milk (RM), thermized milk (TM; 65°C × 15 s), and pasteurized milk (PM; 72°C × 15 s). Heat treatment of the milk reduced the level and diversity of raw milk microflora and extensively or wholly inactivated lipoprotein lipase (LPL) activity. Indigenous milk enzymes or proteases from RM microflora influenced secondary proteolysis in TM and RM cheeses. Differences in FFA in the RM, TM, and PM influenced the levels of FFA in the subsequent cheeses at 1 d, despite significant losses of FFA to the whey during manufacture. Starter esterases appear to be the main contributors of lipolysis in all cheeses, with LPL contributing during production and ripening in RM and, to a lesser extent, in TM cheeses. Indigenous milk microflora and nonstarter lactic acid bacteria appear to have a minor contribution to lipolysis particularly in PM cheeses. Lipolytic activity of starter esterases, LPL, and indigenous raw milk microflora appeared to be limited by substrate accessibility or environmental conditions over ripening.     

EEM fluorescence spectroscopy as a fast method to assess the brine composition of salted herring

Ripening of barrel-salted herring (Clupea harengus) is evaluated by the use of fluorescence spectroscopy and protein determinations. During ripening, protein degradation takes place in the herring and protein is extracted into the brine. The present study aims at identifying parameters which are correlated to the ripening characteristics of barrel-salted herring and which can provide a better understanding of the ripening process. Front face fluorescence landscapes were obtained by measuring directly on the brine from barrel-salted herring. These data were analyzed by parallel factor analysis (PARAFAC), which revealed four fluorophores, tryptophan (two states), vitamin B6 and riboflavin. All four parameters showed an increase in concentration during the storage period corresponding to an increase in protein content that varied from 3 g/100 g at day 60 to 5 g/100 g after 277 days of storage. It was not possible to see a difference in the development of the four fluorophores during the ripening period. The protein content was predicted from the fluorescence landscapes by partial least squares (PLS). The use of unfolded fluorescence spectra gave an RMSECV of 0.26 g/100 g and a correlation between the measured protein content and the predicted values of 0.86.     

Optimisation of osmotic dehydration process of carrot cubes in mixtures of sucrose and sodium chloride solutions

In the optimisation of the osmotic dehydration process of the carrot cubes in mixtures of sucrose and sodium chloride by response surface methodology, using face-centred central composite design (CCF), it was shown that the independent process variables for osmotic dehydration process were osmotic solution concentrations (5–15% w/v sodium chloride in 50 °Brix sucrose syrup), temperature (35–55 °C) and process duration (120–240 min). Statistical analysis of results showed that the linear terms of all the process variables have a significant effect on all the responses. The optimum osmotic dehydration process conditions for maximum water loss, minimum solute gain, maximum retention of colour, and sensory score were: 50 °Brix + 15% w/v sodium chloride solution, 54.8 °C solution temperature and 120 min process duration.     

Effect of storage time and temperature of milk protein concentrate (MPC85) on the renneting properties of skim milk fortified with MPC85

This study investigated the effect of storage temperature (20–50 °C) and time (0–60 days) on the renneting properties of milk protein concentrate with 85% protein (MPC85). Reconstituted skim milk was fortified with the MPC85 (2.5% w/w) and the renneting properties of the skim milk/MPC85 systems were investigated using rheology. It was found that the final complex modulus (final G∗) and the yield stress of the rennet-induced skim milk/MPC85 gels decreased exponentially with storage time of the MPC85 for storage temperatures greater than 20 °C, with a greater effect at the higher storage temperatures. Changes in the solubility of MPC85 with storage time were correlated with the rheological properties. The primary phase of renneting (cleavage of κ-casein) was not affected by the storage of the MPC85; hence the effect was related to the secondary stage of renneting (aggregation/coagulation of rennet-treated casein micelles). Using a temperature–time superposition method, a master curve was formed from the final G∗, yield stress and solubility results. This suggested that the same physical processes affected the solubility and rennet gelation properties of the milks. It is proposed that the MPC85 protein in rennet-treated skim milk/MPC85 solutions may transform from an interacting material, when solubility is high, to an inert or weakly interacting material, when solubility is low, and that this results in the reduced final G∗ and yield stress of the rennet gels when MPC85 is stored at elevated temperatures for long periods.     

The effect of microwave assisted extraction on the isolation of anthocyanins and phenolic acids from sour cherry Marasca (Prunus cerasus var. Marasca)

The aim of this study was to evaluate the influence of microwave assisted extraction on the isolation of anthocyanins and phenolic acids from sour cherry Marasca. A general factorial design was used to study the effect of temperature (from 50 to 70 °C), irradiation time (5–12 min) and microwave power (350–500 W) on individual, total anthocyanins and individual and total phenolic acids. Optimal microwave assisted extraction conditions differed for anthocyanins and phenolic acids, especially in terms of temperature and irradiation time, so lower temperature (60 °C) and shorter time (6–9 min) was more convenient for anthocyanins extraction, while phenolic acids gave higher extraction yield at higher temperatures (70 °C) and longer irradiation time (10 min). The optimal microwave power did not differ significantly for studied compounds, ranging about 400 W. Compared to conventional extraction, microwave assisted one showed higher efficiency for all studied compounds.     

Influence of an adjunct culture of Lactobacillus on the free amino acids and volatile compounds in a Roncal-type ewe’s-milk cheese

Free amino acids and volatile compounds were analysed in a Roncal-type cheese made from pasteurized ovine milk with and without an added adjunct culture (Lactobacillus paracasei + Lactobacillus plantarum). In both batches, the total free amino acid concentration increased 11–12-fold with ripening time, the main amino acids being Leu, Glu, Lys, Phe, Val, and Ile. At the end of ripening, significant differences were recorded for Leu, Ile, Gaba, Phe, Pser, Ser, Gin, Ala, and Orn.     

The effects of salt concentration on conformational changes in cod (Gadus morhua) proteins during brine salting

The effects of different salt concentrations (6%, 15%, 18% and 24% NaCl (w/w)) on the conformational changes of cod muscle proteins during brine salting were examined in this study. Proteins were extracted from the brine salted samples with solutions of 1 M (5.9%) and 4 M (23.4%) NaCl and the quantity of salt soluble proteins (SSP), disulfide bond (S–S), total sulfhydryl (SH) and available SH content in the soluble fraction were determined. Increased salt concentration in cod muscle promoted protein denaturation and aggregation. The SSP and total SH content decreased, whereas the S–S bond and available SH content increased with increased salt concentration in cod muscle. Disulfide bond formation correlated (r = −0.6) with a decrease in total SH groups. Higher SSP and available SH groups of the samples at lower brine concentrations was explained by smaller concentration gradients and salt diffusion rates, resulting in stronger salting-in at early stages of the brining process. There was a significant difference in conformational changes in proteins extracted with a salt solution of 1 and 4 M, mainly due to a different degree of protein aggregation.