Quality Evaluation of “Ricotta” Cheese Produced at Laboratory Level

Ricotta cheese is made from heat-acid precipitation o f p rotein from whey or whey-milk blend. The study aimed to evaluate the quality characteristics of ricotta cheese produced at laboratory level. The chemical composition of ricotta cheese was as follows: moisture: 72.89%, p rotein: 72.89%, protein : 0.14%, fat: 0.6%, ash: 5.37%, pH: 5.28, acid ity: 1.38%, total solid: 18.41%, Ca: 225mg/100g, K: 120mg/100g and Na: 106mg/100g. On the other hand, the total viable count was 1.0×10 c.f.u/g and yeast and mould count was 2.0×10 c.f.u/g. However, all harmful microorganisms were not detected in cheese samples. The sensory evaluation showed that ricotta cheese was generally acceptable. The study recommends encouraging the local dairy industry to introduce ricotta cheese so as to meet the local need and to use whey in the other dairy products.


1.Introduction
Cheese is the name given to a group of fermented milk products produced throughout the world in great variety of flavors, textures and form. Fo x et al, [1] suggested that there are more than 1000 varieties of cheese world wide . Walter and Hargrove [2] described about 400 variet ies and list the names of a further 400, wh ile Burkhalfer [3] classifies 510 varieties. Cheese making developed recently with the gradual acquiring of knowledge about the chemistry and microbio logy of milk and cheese which makes it possible to gain more control over the cheese making process. Few new varieties have evolved as a result of increased knowledge, but existing variet ies have become better defined and their quality has become more consistent.
The ricotta cheese is a high moisture soft cheese [4]. This cheese can be produced from whey or milk or mixture of both [5]. Ricotta cheese is very mild and it is used in many Italian dishes. Several methods have been developed for utilizat ion of whey; one of these methods is the manufacture of ricotta cheese. Ricotta cheese, which means "re cooked", is produced by bo iling acid ified cheese whey [6]; [7]. A ll whey protein cheese mixture are ho mogenized and heated at 93 o C/15-30 min. The curd is left in the whey for 10 min. and then scooped in plastic frame lined over a drainage table and allo ws to achieve complete drainage in 24 hr. The curd is placed in plastic container and stored at 4℃.
Ricotta cheese is not known or consumed largely in Sudan, and few data is available in this type of cheese, therefore the objectives of the present study were: to evaluate the chemical and microbiological characteristics of whey, to produce of ricotta cheese at laboratory level using whey and to evaluate the microbio logical, chemical and sensory quality characteristics of the manufactured ricotta cheese.

Preparati on of Whey Samples
The whey samples were collected fro m local market in Wad Medani, central Sudan during April-May 2011. Whey samples were p laced in plastic containers and transported to the Department of Food Science and Technology laboratory, Faculty of Engineering and Technology, University of Gazira at cool temperature (at 6℃).

Chemical Analyses of Whey
The pH of whey was measured using digital pH meter (PN9410.GL. Britain). The pH meter was calibrated with buffers of p H 4 and 7. The p H values were recorded according to AOAC [8].
The titrimetric determination of acidity of whey was accomplished according to the AOAC [9] method. 10 ml sample were taken, and then diluted in 100ml distilled water, then 10ml were pipetted into two 100ml conical flask. The pipettes were washed with distilled water, and six drops of phenolphthalein indicator then added. The samples were then titrated with 0.1 N. NaOH until a stable pink color was formed. The t itrable acidity was expressed as % lactic acid fro m the fo llo wing formula: Whey and cheese titrable acid ity ml of NaOH 0.1 90 100 % Weight of the sample 100 Where 90 is the amount of lactic acid reacted with 1.0ml of o.1 N NaOH.
The moisture, ash and protein contents of whey samples were determined according to AOAC [8], wh ile fat content of was determined according to the AOAA [9] using Gerber tube. The solid non fat content in whey was determined by using the following formula: Total solid% -fat%

Microbi ological Analyses
Ten ml of whey were ho mogenized with 90 ml of d istilled water by shaking for several minutes, fro m this suspension; 1 ml was taken fro m the dilut ion and transferred to another tube to make serial d ilution up to 10 6. Total viable count per ml was determined by pour plat ing of suitable dilution on melted nutrient agar, and incubated aerobically after solidification at 37℃ for 72 hour [10].
Yeast and Moulds were enumerated according to Harrigan and MacCance [11] using potato dextrose agar (PDA). The plates were incubated at 25℃ for 3-5 days, plates containing between 30 and 300 colonies were count as colony forming units (cfu/ml).
Colifo rm bacterial count was determined accord ing to Harrigan and MacCance [11] using MacConkey broth. The tubes were incubated at 37℃ for 48 hours. Positive tubes gave gas in Durham tubes. Then the positive tubes were sub cultured into EC b roth med iu m and then incubated at 44℃ for 24 hours, to determine coliform bacteria, the tubes showing gas production were considered positive.
Plates showing positive coliform were subjected to the confirmed test for E. coli using Brilliant green bile broth in test tubes with Durham tube. The test tubes were then incubated at 45℃ for 48 hours. Each confirmed positive tube was sub-cultured into E.C broth media and then incubated at 45℃ fo r 24 hours. Tubes showing any amount of gas production were considered to be positive [12].
For salmonella detection, 100 ml of samp les were incubated at 37 o C for 24 hours. Then 10 ml were drawn aseptically and added to 100 ml selen ite broth. The broth was incubated at 37 o C for 24 hours. Then with a loopful streaking was done on dried Bis muth sulphite agar plates. The plates were then incubated at 37℃ for 72 hours. Black metallic sheen discrete colonies indicated the presence of salmonella. A confirmatory test was carried out by taking a discrete black.

Preparati on of Ricotta Cheese at Laboratory Level
Ricotta cheese was made fro m heated acid precipitation of protein fro m whey. During heating by using a heater (at 79℃), 7 liters of whey protein were coagulated. The rate of coagulation increases as temperature was raised to 93℃ and thick layer of curd was formed on the surface of the whey. When coagulation was completed and the curd was firm (after 10-20 min. at 93℃), the curd was removed fro m the heater ordinary plastic mesh.10 ml of lemon juice were immed iately added to the resulting curd. After 10 minutes, the mixture was placed in cheesecloth for 2-3 hours. The obtained ricotta cheese was then kept in small plastic container.

Cheese Yiel d
The resulting cheese was weighed immediately using a weighing balance. The yield of cheese was calculated as follows:

Assessment of Ricotta Cheese
The quality of laboratory made ricotta cheese was determined using chemical, microbio logical and sensory methods.
The pH, acid ity, total solid, solids non fat, moisture, protein, fat and ash were determined as described for the whey.
The microbio logical analyses total viable count, yeast and mould count, coliform count E. coli and salmonella were determined as described for the whey.

Sensory Evaluati on of Laboratory Made Ricotta Cheese
The ricotta cheese was subjected to sensory evaluation using 10 panelists. The panelists were asked to rate or to judge samples to be tasted under 9 scales, about the appearance, texture, colour, flavour and the overall acceptability. Each panelist was provided with water for rinsing. The samp les were g iven codes before being tested.

Statistical Analyses
All scores of sensory evaluation were analyzed by the analysis of variance according to SAS [13]. To determine whether there were significant differences between means for each variable; least significant difference (LSD) test was used.

Chemical Compositions of Whey Sample and pH
Table (1) shows the chemical co mposition of whey samples. The mo isture content was 92.20+0.23%. This value was slightly lower than that found by Kosikowski (1979), which was 93.7%. The protein content was 0.7+ 0.14%, which was lower than that reported by Abozaid [14] who determined a value of 0.9%. The fat content was 0.7+0.1%, which was higher than that reported by Kosikowski [15], which was 0.3%. The ash content of whey is 5.37+0.19%.
This value was higher than that found by Kosikowski [15], which was 0.52%. p H value of whey was 5.1+0.30%. This value was higher than that reported by DTU National Food institute [16], which was 5.00.The titratable acidity (expressed as% lactic acid) o f whey was 2.35+0.3%. This value was higher than that of http: //www. Dairy forall.co m[17], which was 0.4%. The total solid content was 17.9+0.06%. This value was higher than that reported by http: //www. Dairy forall.co m[17], wh ich was 10.5%.

Chemical Composition of Laboratory-Made Ricotta Cheese
The chemical co mposition of laboratory-made ricotta cheese was presented in Table (3). The moisture content cheese was 72.89+2.6% which was lower than that of whey (92.20+0.23%). This reduction could be attributed to the effect of high heat treatment wh ich evaporated part of water. However, the result obtained in the present study was lower than that reported by http:www.Dairy forall.co m[17], which was 93% for ricotta cheese.
The protein content of laboratory-made ricotta cheese was 0.6+ 0.1%, wh ile it was 0.7%+0.14% in whey. The result was lower than that reported by DTU National Food institute [15], wh ich was 0.8% for ricotta cheese. The fat content of laboratory-made ricotta cheese was 0.6+ 0.1%, while it was 0.7+0.1% in whey. The difference did not exceed 0.1. The result was lower than that reported by DTU National Food institute [16], which was 0.8% for ricotta cheese.
The ash content of laboratory-made ricotta cheese was 5.37 + 0.19%, wh ile it was 6.9+1.4% in whey.
pH value of laboratory-made ricotta cheese was 5.28+0.23%, wh ile it was 5.1+0.3% in whey, and this difference could be attributed to the effect of heat treat ment which eliminated the microbial load. The result was similar to that reported by DTU Nat ional Food institute [16], who found value of 5.00% for ricotta cheese.

Microbiol ogical Characteristics of Laboratory-Made Ricotta Cheese
Microbiological analyses of laboratory-made ricotta cheese, as shown in Table (4) revealed presence of 1×10 4 cfu/ml of total viable count. This result was lower than that found by Rossetti et al., [19], wh ich was 2.8 ×10 6 cfu/ml.
The lower levels of total bacterial count in laboratory-made ricotta cheese could be attributed to the effect o f heat treatment which suppress the growth of microorganisms, and also could be attributed to the proper hygienic conditions of cheese production.
The yeasts and moulds count of laboratory-made ricotta cheese was 2×10 2 cfu/ ml. This result was lo wer than that found by Rossetti [19], which was 8.0 ×10 3 cfu/ml. The lower levels of yeasts and moulds count of laboratory-made ricotta cheese were probably due to the effect of higher heat.
Colifo rm, E. coli and salmonella were not found in laboratory-made ricotta cheese.
The absence of Colifo rm, E. coli and salmonella in laboratory-made ricotta cheese, were probably due to the effect of heat treat ment of whey used for the production of ricotta cheese which suppressed the growth of those microorganis ms (pathogenic bacteria).

Sensory Evaluati on
Table (5) su mmarizes the mean scores for sensory attributes of the ricotta cheese, Gibna Bayda and lavachequirit. The result indicated slight differences of the various sensory parameters of cheese samples. There were significant differences p < (0.05) of ricotta cheese color and 111lavor when compared with those of Gibna Bayda an d lavachequirit. The low scores of 111lavor may be attributed to the distraction of certain LA B responsible for generation 111lavor co mpound as a result of heat treatment.
Generally, the panelist highly accepted ricotta cheese when co mpared to Gibna Bayda and lavachequirit. However, there were no significant differences in appearance, texture and overall of the various cheese types.

Conclusions
In the present study the ricotta cheese was prepared at laboratory level using whey wh ich was collected as a byproduct of Gibna Bayda industry. The manufactured ricotta cheese was analyzed chemically, microbio logically and subjected to sensory analysis. Chemical analysis of the manufactured ricotta cheese showed that its main component were 72.89% mo isture, 0.6% protein, 0.7% fat, and 6.9% ash.
Microbial analysis showed that ricotta cheese is free from pathogenic bacteria. The sensory analysis indicated that the ricotta cheese made fro m whey was highly acceptable by panelist.
Fro m the results of this study it is highly reco mmended to introduce whey to other food industries, and to encourage the local industry to increase the production of Ricotta cheese so as to meet the local need.