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A Study on the Effect of Physico-Chemical Characteristics, Palatability and Storage Quality of Kibbles Incorporated With Slaughter House By-products for Canine

Kuleswan Pame Sathu. T. Vasudevan V.N. Prajwal S. and Gunasekaran
Vol 7(8), 228-237

Shelf stable pet kibbles (SSPK) for adult dogs were standardized by incorporating meat-cum-bone meal (MCBM), offal and rendered fat (RF) by baking at 1500C for 50 min. The pet kibbles were packed in PE/Al/PA laminated pouches stored at ambient temperature up to 60 days. The addition of MCBM and RF improved the overall nutrient quality, cooking yield and palatability compared to control. Palatability attributes and preferences were prominently higher for SSPK compare to control. Thio Barbituric Acid Reacting Substances (TBARS), Tyrosine value (TV, Total Viable Count (TVC) and Yeast and Mold count significantly increased with advancement of storage period in both control and SSPK. However the increase in TBARS, TV and microbial load did not adversely affect the palatability attributes. From the study, it can be inferred that pet kibbles with good nutritive value, palatability and stability with lower cost can be prepared by incorporating slaughter house byproducts.

Keywords : Pet Kibbles Meat-Cum-Bone Meal Rendered Fat Shelf Life


The global pet population is increasing at a robust pace especially due to a steady rise in nuclear family. Majority of the pet owners are adopting dogs due to need for security and companionship. With liberalization of economic policies, increasing urbanization, influence of media and awareness of the owners about nutritionally balanced pet food increasing the demand for pet foods. Indian pet food industry is expanding tremendously in the past few decades. Pet owners are started shifting from conventional feeding of scrap and home food to commercially prepared pet foods, which are generally perceived to be more nutritious, better ease in service and more palatable. Moreover home-made pet diets are mostly deficient in protein, energy, calcium, phosphorous, vitamins and micro-minerals, as these foods are often crudely balanced and may not achieve satisfactory palatability, digestibility or safety as required for a dog. The ever rising cost of commercially available pet foods has necessitated the development of cheap as well as nutritious food, by use of slaughter house primary and secondary byproducts. Such as Meat Cum Bone Meal (MCBM), Rendered Fat (RF) and slaughter house byproducts are almost universally used in pet foods. Generally, they provide high quality protein with a good balance of amino acids and minerals of high nutritional quality. But the heat destroyed components in rendered materials are biologically less acceptable and it gets rancid easily, therefore application of these components and oxidation issues are the most common challenges faced in their uses as ingredients in pet foods. Hence this study was undertaken to standardize the formulation and processing condition for the preparation of pet kibbles for dogs using slaughter house byproducts and to assess the effect of optimum level of meat-cum-bone meal and rendered fat on the storage stability of pet kibbles at ambient temperature.

Materials and Methods

Raw Materials

MCBM and RF prepared by dry rendering of bovine primary byproducts were procured from Meat Technology Unit, (MTU) College of Veterinary and Animal Sciences, Thrissur, Kerala, India. Fresh hot deboned lean buffalo meat from the round portion of adult carcass, after trimming external fat and fascia was procured from MTU and stored at 4±10C for 24 hours for conditioning, then frozen until further use. The offal’s of buffaloes were procured from MTU, were washed and stored under frozen condition at -180C until further use. The cereals flours, black gram husk and wheat bran were procured from local market at Thrissur, Kerala. Collagen peptide (food grade) was purchased from Nitta Gelatin India Limited Kochi. The pet kibbles were prepared as per the formulation given in Table 1.

Table 1: Formulary for the preparation of developed pet kibbles

S. No. Ingredients Control (%) SSPK (%)
1 Cereals flour mix 33.0 33.0
2 Buffalo meat 25.0 25.0
3 Offal 20.0 20.0
4 Water 11.25 11.25
5 Black gram husk 4.0 4.0
6 Wheat bran 4.0 4.0
8 Bovine collagen peptide 1.0 1.0
9 Salt 0.5 0.5
10 Turmeric powder 0.5 0.5
11 Brewer’s yeast 0.5 0.5
12 Potassium sorbate 0.2 0.2
13 BHT 0.05 0.05
14 Meat cum bone meal (MCBM) Nil *20
15 Rendered Fat (RF) Nil *5

*MCBM and RF were added over and above the control formulation as suggested by the model design for developed pet kibbles.

Physico- Chemical Properties


The pH was determined using a combined electrode digital pH meter μ pH system 362, Systronics, India) as per procedure of Troutt et al., 1992.

Determination of Water Activity (aw)

For determination of water activity the pet kibbles samples were crushed suitably and filled in the sample cup upto the mark. The filled sample cup was kept in the measurement chamber of Labswift aw meter (Novasina, Switzerland). The readings were taken when the stable water activity was shown in the display.

Hunter Lab Colour (L*a* b*)

Colour of the baked pet kibbles was determined objectively as per Page et al. (2001) using Hunter Lab Mini Scan XE Plus Spectrophotometer (Hunter Lab, Virginia, USA) with diffuse illumination. The L* value gives a measure of the lightness of the product colour from 100 for perfect white to 0 for black, as the eye would evaluate it. The redness/greenness and yellowness/blueness are denoted by a* and b* values respectively (Navneet and Shitiji, 2011).

Cooking Yield Per Cent

The weights of baked kibbles was recorded before (raw weight of dough) and after baking of pet kibbles. Per cent cooking yield was determined by calculating weight differences for sample before and after baking according to Berry and Wergin, (1992)

Product Yield (%) = Wt. of baked kibbles X 100

Wt. of raw dough

Quality Analysis

The moisture content was determined by hot air oven drying, protein by automatic Kjeldhal method, fat by Soxhlet extraction with petroleum ether and total ash by muffle furnace as described in AOAC, (1990). The gross energy was found out by the equation; GE= (Protein x 0.24) + (Fat x 0.38) + (Carbohydrate x 0.17) Kienzle et al. (1998). The calcium and phosphorus was estimated using atomic absorption spectrophotometer, AOAC (1990). Thiobarbituric acid (TBA) value was estimated by extraction method described by Witte et al. (1970) and was expressed as mg malonaldehyde per kg of pet food. The procedure of Strange et al. (1977) was followed for the tyrosine value with slight modificationsThe microbiological quality of pet foods was assessed in respect of total viable count (Morton, 2001), yeast and mold count as per the method prescribed by (Beuchat and Cousin, 2001). Bacterial count was expressed as log10 cfu/g sample.

Palatability/Acceptability and Preference Assessment

The preference of the kibble samples were evaluated based on intake ratio [A/ (A+B)] (Griffin et al., 1996). Dogs with respect to similar age group of three to four years in Labrador and German shepherd breed with similar managemental practice were selected for the palatability assessment. Each dog was offered 180 g of control and SSPK samples 3 to 4 hour after the normal feeding in two separate bowls. The position of the feeding bowls was changed randomly to avoid bias on site preference. Forty different preference tests were performed. The dogs were allowed to feed for 15 min and during this time if one bowl was emptied or rejects, then the two bowls were removed and the leftovers of kibble were recorded.

Cost of Production

Cost of production of SSPK was determined and compared with control. The major determinants of product cost were raw materials including miscellaneous cost such as labour cost and electricity cost. The cost of production was calculated based on the prevailing market cost of the raw materials and various ingredients used in the formulation. The cost of production of SSPK was Rs 170.00 per kg compared to Rs. 173.00 for control. The production cost of SSPK was lower than control due to the higher yield per cent.

Statistical Analysis

The preparation of pet kibbles and proximate composition was repeated six times and the acceptability/palatability was studied using 20 nos. of homogenous dogs over a period of 20 days per replication and the data were statistically analyzed as per Snedecor and Cochran (1994) and Siegal (1956) by using SPSS software version 21.0

Results and Discussion

Physico-Chemical Properties and Proximate Composition

The physico-chemical properties and proximate composition of SSPK compared with control are shown in the Table 2.

Table 2: Physico-Chemical characteristics and proximate composition of control and SSPK

Parameters Control SSPK Significance
pH 5.46±0.03 5.32±0.02 NS
Water activity (aw) 0.54±0.08 0.54±0.02 NS
Cooking yield (%) 56.81±0.46 66.70±0.53 **
Moisture (%) 9.77±0.11 10.31±0.17 **
Dry matter (%) 90.29±0.10 89.68±0.17 **
Crude protein (%) 18.08±0.34 21.91±0.43 **
Fat (%) 6.49±0.24 14.97±0.35 **
Crude fiber (%) 3.48±0.09 3.45±0.06 NS
Total ash (%) 6.52±0.12 7.43±0.20 *
Calcium (%) 2.06±0.03 2.24±0.09 NS
Phosphorus (%) 1.04±0.08 1.17±0.06 NS
Carbohydrate (%) 59.12±0.47 46.16±0.77 **
NFE (%) 55.64±0.48 42.71±0.76 **
GE (Kcal/100g) 1683±0.07 1859±0.07 **

Control (Pet kibbles without MCBM and RF) and SSPK- (Pet kibbles with C+ 20% MCBM + 5% RF). NS- Non Significant, *p<0.05, **p<0.01

The cooking yield of the SSPK was significantly (p<0.01) higher than control. The higher cooking yield in SSPK could be due to synergistic effect of MCBM and fiber ingredients to bind more water during baking process. The moisture, dry matter , protein, fat, ash and GE (Kcal/100g) content were significantly (p<0.01) higher in SSPK compared to control The higher protein and fat content in SSPK could be due to proportionately higher moisture, as well as higher cooking yield due to addition of MCBM and RF. Urling et al. (1993) also observed significant increased in the protein, fat and ash per cent in pet foods with addition of slaughter house byproducts in the form of RF, MCBM and blood in the pet foods. The average energy content in 100g of control and SSPK samples were 1683 and 1859 kcal respectively. The significantly (p<0.01) higher energy content in SSPK was attributed to higher fat content in SSPK on addition of RF. This result supported the finding of Hoelscher et al. (1987), who reported fat content and calorie content positively co-related. The nutrient profiles of both the control and SSPK were in line with the (AAFCO, 2007) recommendation on dry matter basis for adult dog.

Colour Characteristics (L*a*b* values)

The colour characteristics of the control and SSPK were measured objectively in terms of L*, a* and b* values (Table 3). The redness value (a*) significantly (p<0.05) decreased on addition of MCBM and RF, which might be due to dilution of meat pigment concentration leading to decrease in redness value and lower dispersion of the cereals flour mix in the products. This observance was in accordance with Claus et al. (1989), who found that the meat products with low fat level could favour the appearance of dark colour (higher redness value).

Table 3: Effect on Colour (Hunter L*a*b*) of Control and SSPK

Parameter Control SSPK Significance
L* (lightness) 30.70±0.43 31.60±0.35 NS
a* (redness) 7.85±0.15 6.08±0.13 *
b* (yellowness) 21.12±0.46 20.42±0.20 NS

Control (Pet kibbles without MCBM and RF) and SSPK- (Pet kibbles with C+ 20% MCBM + 5% RF), NS- Non Significant, *p<0.05

Palatability-Preference and Intake Ratio

It was observed that the owner’s preference attributes (odour, colour and appearance) and palatability attributes by dogs towards SSPK was highly distinguishable from that of control pet kibbles (Fig.1 a).

Fig.1: Comparison between Control and Standardized pet kibbles on (a) Different palatability attributes on dog and dog owners (b) Intake ratio on dogs

The intake ratio (IR) of SSPK was significantly (p<0.05) higher compared to control samples (Fig. 1b). The IR of SSPK scored 64 per cent and control pet kibble scored 36 per cent. From the observation of palatability attributes scores and intake ratio per cent it can be inferred that pet kibbles containing 20 per cent MCBM and 5 per cent RF was having higher palatability and overall preference than control. It might be due to the better flavour and texture in SSPK due to the addition of MCBM and RF. These findings agrees with those of Dust et al. (2005), who reported that the use of animal protein and fat in the pet foods, improved the palatability, enhanced its physical attributes and owners preference.

Storage Stability of Shelf Stable Pet Kibbles

The TBARS values of control and SSPK (Fig. 2) significantly increased (p<0.05) from 0.31-4.45 and 0.89-5.15 mg malonaldehyde/kg pet kibble during storage period.

Fig. 2: TBARS values of Control and SSPK on storage period of at ambient temperature

Similar increase in TBARS value was also reported in dog pet foods added with dry rendered spent hen meal during the storage period Rajendra Kumar et al. (2011). Tyrosine value of both control and SSPK increased significantly (p<0.05) during storage period (Fig. 3).

Fig. 3: TV of Control and SSPK on storage period at ambient temperature

TV of control increased from 28.89-103.44 and that of SSPK 37.59-104.92 mg tyrosine/ 100 g kibble. The increase in the TV on storage might be due to the protein breakdown by chemical and microbial action. Similar result with increased of TV on storage have been reported by Karthik et al. (2010) in spent hen meal based pet food prepared by extrusion. Dainty et al. (1975) opined that the increase in concentration of tyrosine occurs due to microbial proteolytic enzymes action on protein substrate. Total viable count increased from log10 2.10-7.56 cfu/g in control and 3.79-7.67 cfu/g in SSPK (Fig. 4); whereas Yeast and mold increased from log10 1.90-6.03 cfu/g in control and 1.98-6.99 cfu/g in SPK (Fig. 5).

Fig. 4: Growth trend of TVC of Control and Standardized pet kibbles on storage period at ambient temperature Fig. 5: Growth trend of Yeast and mould of Control and Standardized pet kibbles on storage period at ambient temperature

Similar increase in the microbial count was reported by Karthik (2007) in dry pet food prepared by incorporating poultry byproducts meal. The significantly (p<0.05) higher TVC and Yeast and mold count noted in SSPK compare to control throughout the storage period might be due to less heat penetration due to more fat content in SSPK, and more nutrient content available (Table 2.) for the microbes due to addition of MCBM and RF in SSPK might have favoured the microbial growth. Wirth (1972) reported that low fat products have better shelf life than full fat products due to more heat penetration in low fat products.

Cost of Production

The cost of production of shelf stable pet kibbles with 20 % MCBM and 5% RF levels worked out to be Rs. 170.00 per kg. The cost of commercially available pet foods ranged from Rs. 200 -220/kg. The SSPK in this study have the nutritional profile in line with the standards of AFFCO (2007) recommendation for adult dog food. Hence it can also be marketed as pet food at a cost lower than the commercially available pet foods.


Shelf stable pet kibbles with good nutritive quality and palatability to dogs can be prepared by incorporating 20 % MCBM and 5 % RF, which can be safely stored up to 60 days at ambient temperature in PE/Al/PA laminated pouches. A lower production cost of the pet kibbles prepared in the present study compared to the commercially available pet foods is an inductive of its good market potential. Utilization of slaughter house byproducts in pet food preparation may reduce the environmental pollution and gives better returns.


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