THE EFFECT OF INTENSE LIGHT PULSES ON THE SENSORY QUALITY AND INSTRUMENTAL COLOR OF MEAT FROM DIFFERENT ANIMAL BREEDS

: Intense light pulses (ILP) are an emerging processing technology, which has a potential to decontaminate food products. The light generated by ILP lamps consists of a continuum broadband spectrum from deep UV to the infrared, especially rich in UV range below 400 nm, which is germicidal. Evaluation of the effect of intense light pulses (ILP) on sensory quality of meat, game and poultry was performed using two kinds of red meat (beef and pork), two kinds of poultry (chicken and turkey) and three game meat samples (deer, rabbit and kangaroo). All the samples were treated with 1 and 5 light pulses (pulse duration of 300 µs and pulse intensity of 3.4 J/cm 2 ) at a rate of one pulse per 2 seconds. Sensory quality changes induced by intense light pulses were different and depended on animal species, type of meat and ILP dose applied. Only the odour of all the meat, poultry and game samples suffered significant changes after the pulsed light treatment. Of all kinds of meat investigated only turkey received scores below the good quality grade after the treatment. Instrumental colour values remained unaffected in chicken and rabbit meat samples while higher doses of ILP significantly compromised both redness and yellowness only in pork and turkey meat.

The inactivation mechanism of ILP is similar to that of continuous UV-C light; it causes the formation of thymine dimmers which renders microbial cells unable to replicate; this is called the photochemical effect (Gómez-López, 2012).Additionally, photophysical and photothermal effects have been identified (Krishnamurthy et al., 2010).Its big advantage is that it can inactivate microorganisms very fast.Different studies have demonstrated the sensitivity of bacteria to ILP on meat (Hierro et al., 2012), poultry (Keklik et al., 2010;Paskeviciute et al., 2011) meat products (Ganan et al., 2013;Hierro et al., 2011), meat contact surfaces (Rajkovic et al., 2010) and seafood (Cheigh et al., 2013;Ozer and Demirci, 2006).However, if microbial inactivation is a critical requirement, it is also essential to keep the nutritional and sensory properties of the product, minimizing the possible loss of quality caused by the treatment (Hierro et al., 2012).
The aim of this study was to systematically evaluate the effect of intense light pulses (ILP) on sensory quality and color of 7 different varieties of meat, game and poultry.

Samples preparation
Two kinds of red meat (beef and pork), two kinds of poultry (chicken and turkey) and three game meat samples (deer, rabbit and kangaroo) were used in this study.All of the samples used were purchased from a local retailer and kept refrigerated at 2±2°C until treated.All the fresh meat, poultry and game was cut into 10 cm chunks before the ILP treatment.

ILP equipment and treatment
The ILP treatments were performed using a laboratory-scale batch-fed pulsed-light system unit: Tecum -Mobile Decontamination Unit (Claranor, Manosque -France).Light pulses with duration of 300 µs and pulse intensity of 3.4 J/cm 2 , measured with SOLO 2 -Power and Energy Meter (Gentec Electro-Optics, Inc., Quebec, Canada), were generated by four 20 cm cylindrical Xenon flash lamps (Flashlamps Verre & Quartz, Bondy, France), with an input voltage of 3000 V.
The samples were ILP-treated with 1 pulse (1P) and 5 pulses (5P) at a rate of one pulse per 2 seconds, respectively.During treatments, samples were placed in the system unit at a distance of 6 cm from the top and bottom lamps, and 10 cm from the left-hand and right-hand lamps.No treatment was applied to the control groups of samples.

Sensory Analyses
Sensory evaluation was performed by a professional panel of eight panelists, members of the Department of Food Safety and Food Quality-University of Ghent, Belgium and of the Meat Science and Technology Department-University of Belgrade, Serbia.The panel was trained according to international standards (ISO, 1993) and additionally trained for three days in the sensory assessment of meat and meat products by a panel leader with over 2,000 h of sensory testing experience of meat and meat products.
Sensory tests were performed in a controlled sensory analysis laboratory (Food Safety and Food Quality Department/University of Ghent -Belgium) built in accordance to the general guidance for the design of test rooms intended for the sensory analysis of products (ISO, 2007) with individual booths equipped with computer terminals and provided with red light to mask any differences in color when needed.

Five-Point-Scale Scoring Method
The test was carried out as described by Tomic et al. (2008) with slight modifications.Selected sensory attributes (Table 1) were assessed using the 5-point scale with the following descriptions: 5=(excellent, typical quality, without visible defects); 4=(good quality, with minimal visible defects); 3=(neither good nor poor quality, still can be used for its intended purpose); 2=(poor quality, reworked could be used for its intended purpose); and l=(unacceptable, extremely poor quality, cannot be used for its intended purpose), with ability of giving semi scores (4.5, 3.5, 2.5 and 1.5).Scores given to each of assessed attributes were corrected by corresponding coefficients of importance (Table 1).Coefficients of importance (CI) show the relative importance of a single sensory attribute to the total sensory quality.Sum of all CIs is arranged to be 20, and in that way the sum of corrected scores gives the "percentage of total sensory quality" in a given situation.Dividing the total value by the sum of CI gives the "pondered average value of total sensory quality".A section in the score card was included for panelists to leave their comments.

Instrumental color measurement
Instrumental color readings of samples were measured using a Konica Minolta spectrophotometer CM-2500d (Konica Minolta, Osaka, Japan), operating in the CIE L*a*b* color space.The L* (lightness), a* (redness) and b* (yellowness) values (a single repetition) were determined from the mean of 10 random readings on the surface of each sample, using D 65 illuminant and 10° standard observer.The measurement was repeated in triplicate (n=3) and the values averaged.The instrument was calibrated with a white calibration tile and black calibration box.Data acquisition was performed using the Spectramagic NX color data software, version 1.52 (Osaka, Japan).

Statistical analysis
Data entry and decoding were 100% verified.A one-way ANOVA was conducted to compare the results of the different assays, using SPSS Statistics 17.0 (Chicago, Illinois, USA) data analysis software.An alpha level of p<0.05 was used to determine significance.

Results and Discussion
Five-Point-Scale Scoring Method ILP treatment did not significantly change (p<0.05)appearance and total score values of the beef samples (Table 2).The color score also remained unchanged regardless of the level of fluence applied which is in contrast of the findings of Hierro et al. (2012) where the color of beef was assessed by panel members as slightly lighter after the treatment of 11.9 J/cm 2 .The application of 1 pulse (3.4 J/cm 2 ) in our investigation significantly decreased score for odor of beef while the same happened only after 8.4 J/cm 2 when applied to beef carpaccio in the experiments of Hierro et al. (2012).The similar in both investigations was the fact that the beef odor was assessed as acceptable in both cases even after the highest fluency rate applied.According to our results the odor of beef meat is a bit more sensitive to the ILP then the odor of pork meat, because the odor scores for pork meat have significantly decreased only after the 5-pulses treatment.For the poultry, the only sensory attribute affected by the ILP treatment was odor but not to such extent that could also affect the pondered average values of the total sensory quality for the chicken and turkey meat (Table 2).Similar was found by Paskeviciute et al. (2011) where UV light dose higher than 6 J/cm 2 had only some moderate effect on odor of chicken.The odor scores significantly decreased in all game meat samples after the 5-pulses treatment but they were most easily observable in deer meat and essentially contributed to the significant change of its pondered average value of total sensory quality.The effect of the treatment on odor was least pronounced in kangaroo meat.The panelist's comments were unanimous that the effect of ILP on game meat was reflected only by subtle changes in its naturally sour odor.

Instrumental color measurement
The instrumental color values of beef meat were not affected by 1-pulse treatment, since no significant differences (p>0.05) were observed (Table 3).Treatment of 5 pulses significantly decreased redness in beef, while no significant differences were observed for lightness and yellowness.In beef carpaccio subjected to ILP, Eva Hierro et al. (2012) also observed decrease in a * values but they were followed with the significant differences in b * value when the samples were treated with fluences equal to or higher than 8.4 J/cm 2 .Values in the same column with different letter are significantly different (p<0.05) The same was the case in our investigation with the pork meat treated with 17 J/cm 2 when both values, a* and b*, significantly decreased after the treatment.Chicken color values were not significantly changed (p>0.05)irrespective of the level of treatment.This is in agreement with the results of Keklik et al. (2010) indicating that mild and moderate pulsed light treatments also did not affect the color of chicken samples (p>0.05),although extreme ILP treatment did increase the lightness (L * ), redness (a * ), and yellowness (b * ) of samples significantly (p<0.05).The a * value of treated turkey samples were significantly lower than that of the untreated samples with the significant difference observed among the fluences assayed.The redness gradually decreased as fluence increased.The yellowness was found significantly lower to control samples only after the treatment of 5 pulses.Similar ILP color resistance to the one of chicken meat, in our experiment, was observed only in rabbit meat samples (Table 5).Dear meat suffered significant decrease in redness value after the 5-pulses treatment while the kangaroo meat was significantly lower in L * (after 1 pulse) and in b * (after 5 pulses).

Conclusion
Our study indicated that the sensory quality changes induced by intense light pulses are different and depend on animal species, type of meat and ILP dose applied.Only the odor of all the meat, poultry and game samples suffered significant changes after the pulsed light treatment.Of all kinds of meat investigated only turkey received scores below the good quality grade after the treatment.Instrumental color values remained unaffected in chicken and rabbit meat samples while higher doses of ILP significantly compromised both redness and yellowness only in pork and turkey meat.

Table 2 . Sensory evaluation scores (mean±SD) for 5-Point-Scale Scoring test of the ILP treated meat, poultry and game
Values in the same column with different letter are significantly different (p<0.05)