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International Journal of Food Properties

ISSN: 1094-2912 (Print) 1532-2386 (Online) Journal homepage: https://www.tandfonline.com/loi/ljfp20

Textural, microstructural, and dynamic rheologicalproperties of low-fat meat emulsion containingaloe gel as potential fat replacer

Yogesh Kumar, S. K. Tyagi, R. K. Vishwakarma & Anu Kalia

To cite this article: Yogesh Kumar, S. K. Tyagi, R. K. Vishwakarma & Anu Kalia (2017) Textural,microstructural, and dynamic rheological properties of low-fat meat emulsion containing aloe gelas potential fat replacer, International Journal of Food Properties, 20:sup1, S1132-S1144, DOI:10.1080/10942912.2017.1336721

To link to this article: https://doi.org/10.1080/10942912.2017.1336721

© 2017 Taylor & Francis Group, LLC

Accepted author version posted online: 08Jun 2017.Published online: 08 Aug 2017.

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Textural, microstructural, and dynamic rheological properties oflow-fat meat emulsion containing aloe gel as potential fat replacerYogesh Kumar a, S. K. Tyagia, R. K. Vishwakarmaa, and Anu Kaliab

aAgricultural Structures and Environmental Control Division, Central Institute of Post-Harvest Engineering &Technology (CIPHET), Ludhiana, India; bElectron Microscopy and Nanoscience Laboratory, Punjab AgriculturalUniversity (PAU), Ludhiana, India

ABSTRACTThe effect of aloe gel (AG) and vegetable oil (VO) as animal fat replacers on thetexture, dynamic rheology, microstructure, and oxidative stability of low-fatmeat emulsions was evaluated. There was no difference in complex viscosity(η*), G’0 - G’’0, and An values between 50% fat replacement and full-fat meatemulsion samples. In all the samples, the G′ values were much higher than G″values with a small frequency dependency. In low-fat meat emulsion (50% fatreplacement) samples, the difference between G’ and G’’ was higher whichsuggested strong matrix network structure. Hardness and springiness valueswere affected (P < 0.05) by addition of AG and were in agreement with dynamicrheological parameters (G’ and G’’). The scanning electron microscopic (SEM)images of meat emulsion samples containing 50% AG showed more regular,compact, and dense continuous phase as compared to other samples. Higheroxidative stability (low TBARs) was observed (P < 0.05) in samples which con-tained AG.

ARTICLE HISTORYReceived 16 January 2017Accepted 28 May 2017

KEYWORDSLow-fat meat product; Aloegel; Dynamic rheology;Microstructure; Textureprofile; TBARs

Introduction

Meat and meat products are good source of essential nutrients with high biological value. The high fatcontent in processed meat products is responsible for desired eating and sensory attributes[1] which areimportant for consumer acceptability. However, these products are often considered as unhealthy byconsumers due to the presence of high saturated fat. The high consumption of saturated fat ispositively correlated with the higher incidence of cardiovascular diseases and other physiologicaldisorders.[2] Thus, the development of low-fat meat products with desired attributes as possessed byfull-fat meat products is a challenge for the meat industry. Keeping this in view, some fat replacers(plant proteins, polysaccharides, extracts, fibres, vegetable oil, gums, etc.) have been identified andused for manufacture of low-fat meat products.

Low-fat meat products have been developed using some non-meat ingredients or plant oils (replace-ment of highly saturated animal fat) like inulin and bovine plasma proteins[3]; pineapple by-product andcanola oil[4]; rice bran oil and malva nut gum[5]; grape seed oil and rice bran fibre[6]; sugarcane dietaryfibre and pre-emulsified sesame oil[7]; fish oil, milk proteins, and carrageenan.[8] However, the additionof non-meat ingredient and/or the substitution of animal fat with plant oil alter the technologicalproperties of meat emulsion. Therefore, the most important factor for manufacture of low-fat meatproducts is to avoid the undesirable quality changes, notably emulsion stability and rheology of the meatproducts.[9]

Aloe plant (Aloe barbadensis miller; Liliaceae) contains aloe gel (AG) in its leafy structures. Theimportance of aloe-based drugs has been reviewed recently.[10] Various polysaccharides like mannans,

CONTACT Yogesh Kumar yogeshsomvanshi@rediffmail.com Agricultural Structures and Environmental Control Division,Central Institute of Post-Harvest Engineering & Technology (CIPHET), Ludhiana, 141004, India.© 2017 Taylor & Francis Group, LLC

INTERNATIONAL JOURNAL OF FOOD PROPERTIES2017, VOL. 20, NO. S1, S1132–S1144https://doi.org/10.1080/10942912.2017.1336721

arabinans, and arabinogalactans are found in the AG which are associated with moisture retentioncapacity, formation of gel structure inside the leaf structures, and other biological activities.[11–13] TheAG can be used for development of various food products without greatly affecting the colour andflavour properties because of its colourless, odourless, and tasteless behaviour. In our previous study, itwas demonstrated that the addition of AG in the meat emulsion resulted in higher or at least similarphysico-chemical, technological, and sensory properties of low-fat meat products.[14] Recently,Soltanizadeh and Ghiasi-Esfahani[15] concluded that aloe vera acted as a hydrocolloid and improvedthe quality of low-meat beef burgers in terms of physicochemical and technological properties.However, the effects of addition of AG have not been studied on the rheological properties, texturalattributes, microstructural relationship with dynamic rheological attributes, and oxidative stability oflow-fat meat emulsion. The objective of this study was therefore to assess the impact of addition of AGin combination with vegetable oil (VO) in various proportions on dynamic rheology, texture profile,microscopic structure, and oxidative stability of low-fat meat emulsions.

Materials and methods

Materials

Fresh broiler chicken meat (6 weeks of age) from breast and thigh region (1:1) was purchased from alocal meat market. All visible fat and connective tissue were trimmed off, and the meat was stored at0°C until it is required for product manufacture. Suitable amount of the meat was partially thawed at4°C prior to meat emulsion preparation. As fat source, commercial soybean oil (Fortune, AdaniWilmar Limited, Gujarat, India) (16% saturated fatty acid, SFAs; 24% monounsaturated fatty acid,MUFAs; and 60% polyunsaturated fatty acid, PUFAs) was used.

AGwas obtained from leaves of Aloe (Aloe barbadensismiller) plant grown locally (approximately 3years of age). The pulp contents were obtained manually as described by Kumar, et al.[14] Heattreatment (65°C for 10 min) was applied to the homogenised AG for improving its functionalproperties and for protecting its biological activity during further processing and storage.[16] AG wasthen cooled and stored at 4 ± 1°C until it is used for product manufacture. AG was taken fresh fromdifferent representative areas and was processed in these similar conditions during various repetitionand replication of experiments. The physical properties (rheological) and chemical composition(carbohydrates/monosaccharide/polysaccharide/protein/acetyl) of AG from Aloe barbadensis millerhave been characterised in previous studies.[17–18] The analysed pH of this AG was 4.31 ± 0.02.

Experimental design and manufacture of low-fat meat emulsion

The emulsion was prepared as described by Choi et al.[19] Four different formulations of low-fat meatemulsion including control were manufactured according to Table 1 in triplicate (three trials each). Themeat was passed through a meat mincer (Sirman, Pieve di Curtarolo, PD, Italy) with a 5 mm hole plate,mixed well by hands, and divided in four equal parts. Each portion was homogenised and ground for 1min in a meat cutter (Scharfen, Germany). NaCl (2%) was added to meat that had been previously

Table 1. Formulation (g) of meat emulsions containing aloe gel (AG) and the vegetable oil (VO) in different proportions.

Samples1 Meat Water NaCl2 AG VO

AGT1 100 10 2 15 –VOT2 100 10 2 – 15AGVOT3 100 10 2 7.5 7.5CT4 100 10 2 – –

1AGT1: formulated with 100% Aloe gel; VOT2: formulated with 100% vegetable oil; AGVOT3: formulated with 50% aloe gel and50% vegetable oil; CT4: without aloe gel and vegetable oil.

The following was also added to all samples: 2.0 g per 100 g NaCl for extraction and solubilisation of muscle proteins.2dissolved in water.

INTERNATIONAL JOURNAL OF FOOD PROPERTIES S1133

dissolved in chilled water (2°C) and then mixed for 1 min in the same meat cutter. AG and VO wereadded to the samples according to the formulations, and the emulsion samples were homogenised for 3min. The final emulsion temperature was below 12°C in all cases. The samples were analysed for variousproperties, either as raw or after steam cooking at 120°C for 20min. For steam cooking, the raw emulsionsamples were filled in the rectangular aluminium boxes of 10 cm × 20 cm dimensions. The differentsamples served as: 100% AG (AGT1), 100% fat (VOT2; Positive control), 50% fat replaced (AGVOT3),without any AG or fat (CT4; negative control for comparison with other three samples). Samples werefilled in LDPE and stored at 4°C for storage studies.

Dynamic viscoelastic characterisation

Rheological measurements were performed on a rheometer (MCR 101, Anton Paar GmbH, Graz,Austria) fitted with 50 mm smooth parallel plate (PP50-SN23970; d=1 mm) geometry runningRheoplus software package (RHEOPLUS/32 V3.40 21005317-33024, Anton Paar GmbH, Germany).Raw meat emulsion was placed onto the centre of the base plate. The upper plate was moved intoposition, that is, the distance between the two plates (gap) was set to 1 mm. Excess material was trimmedfrom the plate edges, and samples were allowed to rest for appropriate time duration to achieve aconstant test temperature (25°C regulated by the rheometer’s Pelltier plate and temperature hood) andfor relaxation of residual stresses. Viscoelastic properties were assessed by performing a preliminaryamplitude sweep to identify the linear viscoelastic (LVE) region of the samples. A frequency sweep from0.1 to 100 Hz was performed, and the results for storage modulus (G’), loss modulus (G’’), and complexviscosity (η*) were recorded. The complex dynamic viscosity (η*) (Pa.s) is used to describe the totalresistance of a material considered to be a viscous liquid.[20] This is an indicator of the overall response ofsamples against the sinusoidal strain calculated by the following equations[21]:

η� ¼ G�=ω (1)

Loss tangent (tan δ) was calculated according to the following equation which denotes relative effectsof viscous and elastic components in a viscoelastic behaviour.

tan δ ¼ G00=G0 (2)

The rheological moduli (G’ and G’’) were modelled using the following power law equations(Friedrich and Heymann 1988):

G0 ¼ G00ω

n0 (3)

G00 ¼ G000ω

n00 (4)

Instrumental texture profile analysis

Texture profile analysis (TPA) was performed in a TA-HDi Texture Analyzer (Stable Micro SystemsLTD., UK), and attributes were calculated as described by Bourne.[22] Three determinations performulation of cooked (120°C for 20 min) meat emulsion (2.5 × 2.5 × 2.5 cm) were compressed to40% of their original height. Force–time deformation curves were derived with a 50 kg load cell applied ata constant crosshead speed of 1 mm/s. Attributes were calculated as hardness (Hd): peak force (N)required for first compression; cohesiveness (Ch): ratio of active work did under the second compressioncurve to that did under the first compression curve (dimensionless); springiness (Sp): distance (mm) ofsample recovery after the first compression; and chewiness: Hd × Ch × Sp (N mm). All texturemeasurements were carried out at room temperature. Texture measurement was done for freshly cookedsamples as well as for stored samples from day zero to day eight to see the effect of refrigerated storageconditions on the textural attributes of various emulsion samples.

S1134 Y. KUMAR ET AL.

Microstructure

Microstructure of fresh raw meat emulsion samples was analysed by scanning electron microscopy(SEM) as described by Kumar et al.[14] The meat emulsion samples were fixed with a mixture of 2.5%glutaraldehyde (2.5 g/100 g) in 0.1 M sodium cacodylate buffer (pH 7.2), post fixed with OsO4, washed,dehydrated in increasing concentrations of alcohol, critical-point-dried, sputter coated with gold in aion sputter coater (Hitachi, E1010), and scanned by SEM (S-3400N; Hitachi, Tokyo, Japan) at 15 kV. Alarge number of micrographs were taken to select the most representative ones.

Estimation of oxidative stability

The thiobarbituric acid reactive substances (TBARS) were determined from day zero to day eight byusing the extraction method[23] to analyse the effect of AG addition on the oxidative stability of meatemulsion samples. Samples (4 g) were homogenised with 20 ml trichloro acetic acid solution (20%), andthe slurry was centrifuged (3000 g) (MP 400R Eltek Ltd., India) for 10min. The supernatants (2 ml) weremixed with equal volume of freshly prepared 0.1% thiobarbituric acid (TBA) in glass test tubes andheated in water bath at 100°C for 30 min followed by cooling under tap water. The absorbance of themixtures was measured at 532 nm, and the TBARS values were calculated using a standard curve andexpressed in mg malonaldehyde/kg.

Statistical analysis

All data were summarised and submitted to one-way analysis of variance (ANOVA). Tukey’s test (P < 0.05)was applied to determine significant differences between treatments.

Results and discussion

Dynamic viscoelastic characterisation

The results of strain sweep test showed that the storage modulus (G’) and loss modulus (G’’) values werealmost independent of the stress-strain within the linear viscoelastic region (LVR), and a further increasein applied stress resulted in a sudden fall of the G′ values which might be due to the rupturing ofmyofibrillar protein–protein interactions (Tabilo-Munizaga & Barbosa-Cánovas, 2005). The samplescontaining vegetable oil (VOT2) and aloe gel+vegetable oil (AGVOT3) were able to withstand a higherstress before rupturing than AGT1 and CT4 samples. The G’ was higher than G” in the LVR region in allthe samples, which indicated that the samples were more elastic than viscous with a network structure[24]

because the G′ reflects solid-like properties of a viscoelastic material, while the G″ reflects liquid-likeproperties.

In the frequency sweep test (Fig. 1), the G′ values were much higher than G″ values over allexperimental ω values with a small frequency dependency in all the samples. Thus, all the samplesshowed typical viscoelastic behaviour with typical ‘weak gel’ properties. This type of behaviour is usuallyshown by a 3D gel cross-linked gel network.[25] Similar results were obtained for low-lipid meatemulsions containing fish oil and different binders,[26] emulsified sausages with added carboxymethylcellulose and microcrystalline cellulose,[27] and low-fat sausage containing inulin,[28] as a fat substitute.Same proportional changes in the G′ and G″ values with frequency over a wide range were seen (Fig. 1) inthe AGVOT3 samples which also suggested that these samples had well organised matrix structure[29]

which provided more stability to the emulsion samples.In general, G’ and G’’ decreased with the increase of AG addition which could be associated with the

increase in the moisture contents (improvedWHC)[14] and the viscous effect of the AG itself. A decreasein storage and loss moduli with increasing hydrocolloid concentration though no changes in loss tangentwas also observed for various meat products.[27] The AGVOT3 samples showed higher G′ at lowerfrequency, bigger difference between G′ and G′′, and a smaller slope of the curve (Fig. 1) as compared to

INTERNATIONAL JOURNAL OF FOOD PROPERTIES S1135

AGT1 samples where the initial G′ values were lower. The G’ values for the AGVOT3 andVOT2 sampleswere non-significant but higher (P < 0.05) than those for the AGT1 samples. Moreover, the differencebetween G’ and G’’was lesser in VOT2 samples as compared to the AGVOT3 samples. The CT4 samplesshowed higher G’ at lower frequency, but the difference between G’ and G’’ was lesser than the AGVO3samples. This indicated that the AGVOT3 samples had the strongest network structure as compared tothe other samples. The tan δ values were nonsignificant among AGT1, VOT2, and CT4 samples butsignificantly more in AGVOT3 samples. Moreover, the higher tan δ values (Table 2) in AGVOT3samples showed that combination of AG and VO resulted in more stable matrix than only AG-containing or only VO-containing samples.

The viscoelastic parameters as obtained by fitting power law equations are presented in Table 2. Thedifference between G’0 and G’’0 as well as the value of An suggests strength of viscoelastic material andrheological unit interaction. These parameters have been used to assess the firmness of gel matrix.[30]

G’0 - G’’0 and An values were highest in the CT4 samples, lowest in AGT1 samples, and in VOT2 andAGVOT3 samples values were intermediate. Values were somewhat similar (lesser difference) inVOT2 and AGVOT3 samples. This suggested that samples with 100% AG were least rigid and firmerthan other samples. The properties of AGVOT3 and VOT2 samples were similar in terms of rigidnessand firmness. This suggested that replacement of VO with AG hadminimal effect on these parameters.It has also been suggested by Delgado-Pando et al.[30] that lower values of G’0 - G’’0 and An resulted inbetter binding properties, and higher values resulted in poor gel quality due to low emulsion stability.

1000

10000

10

100

1000

10000

100000

0.1 1 10 100

G′ a

ndG

” (P

a)

Com

plex

vis

cosi

ty, |

η*|(P

a s)

Angular frequency, ω (s-1)

|η*| - AGT1

|η*| - VOT2

|η*| - AGVOT3

|η*| - CT4

G′ - AGT1

G′ - VOT2

G′ - AGVOT3

G′ - CT4

G” - AGT1

G” - VOT2

G” - AGVOT3

G” - CT4

Figure 1. Frequency sweep test for mechanical spectra: storage modulus (G′), loss modulus (G″), and complex viscosity (η*) ofdifferent meat emulsion samples at 25°C. For sample denomination, see Table 1.

Table 2. Loss tangent (tan δ) and power law parameters (fitted values) for the rheological parameters from frequency sweep test,at 25°C for different samples.

Samples Tan δ1 G’0 n’ R2 G’’0 n’’ R2 G’0-G’’0 An

AGT1 0.274 4001.3 0.0814 0.7528 1179.2 0.1004 0.8199 2822.1 3877.0VOT2 0.281 4534.7 0.0766 0.8347 1358.3 0.0746 0.7913 3176.4 4452.0AGVOT3 0.305 4500.8 0.0687 0.8550 1215.8 0.0841 0.8241 3285.0 4415.4CT4 0.276 6117.8 0.0695 0.8698 1665.1 0.0940 0.8342 4452.7 5999.0

For sample denomination, see Table 1.1at ω = 2.14 (s−1).

S1136 Y. KUMAR ET AL.

In our previous study,[14] it was observed that emulsion samples containing AG showed moreemulsion stability and binding properties, and thus results of rheological parameters in presentstudy (G’0 - G’’0 and An) are consistent with this fact that increase in the value of G’0 - G’’0 and An

resulted in lower emulsion stability (gel quality) parameters.All the emulsion samples showed similar flow characteristic (Figs. 1 and 2), that is, shear-thinning

behaviour in accordance with the power law model. This shear thinning regionmight occur as a result ofstructural breakdown due to oil droplet deflocculation.[31] The complex viscosity of AGT1, VOT2, andAGVOT3 was lower than that of the CT4; however, complex viscosity was non-significant (P < 0.05)between VOT2 and AGVOT3, which suggested no alteration in the viscosity component of AG-addedlow-fat meat emulsion samples.

In the present study, the slopes were positive and almost parallel to each other. The curves were almostqualitatively similar for all the emulsion samples studied at low frequency levels, but slight deviation wasobserved at high frequency levels (Fig. 1). The magnitudes of G’ were always greater than those of G’’without exhibiting no cross-point of G’ and G’’. This is a characteristic feature of weak gels and highlyconcentrated dispersions.[32] The tan δ values at all the frequency were lower than one, which alsosuggested that the samples weremore elastic rather than viscous. Moreover, the lower tan δ values duringfrequency sweep is also indicative of well-organised gel network.[33] In general, this is a characteristicbehaviour of protein-stabilised emulsions because an elastic network occurs due to the occurrence of anextensive bridging flocculation process.[34] Chattong and Apichartsrangkoon[35] stated that weak viscoe-lastic or coagulant gel types with some crosslink density showed this type of behaviour during rheologicalassessment.

Rivas and Sherman[36] indicated that water-soluble meat proteins exhibited important viscoelasticity,which was attributed to the strong interlinking of water-soluble meat protein loops adsorbed on thesurface of adjacent oil drops (Fig. 3, SEM image). Our frequency sweep measurement results were alsoconsistent with the results of Flores et al.[37] who studied pork meat emulsions containing sodiumstearoyl-2-lactylate and carrageenan and reported that the meat emulsion samples exhibited solid-likemechanical spectra in which the storage modulus was much larger than the loss modulus in thefrequency range of 1–100 rad/s. It was also reported by Flores et al.[37] that meat emulsion containingsodium stearoyl-2-lactylate and carrageenan behaved as weak gel.

G’ and G’’ are related to the strength of intermolecular interactions of the emulsions and proteingel matrix while rate of change of these parameters is related to the stability of the matrix. The

1

10

100

1000

10000

0 10 20 30 40 50 60

App

aren

t vis

cosi

ty (

Pa s

)

Shear rate (s-1)

AGT1VOT2AGVOT3CT4

Figure 2. Viscosity as a function of shear rate for different meat emulsion samples at 25°C. For sample denomination, see Table 1.

INTERNATIONAL JOURNAL OF FOOD PROPERTIES S1137

difference of G’ and G’’ is related with the strength of matrix. In the present study, this differencewas larger in AGVOT3 samples which showed stronger intermolecular interactions and a morestable matrix. The addition of AG with the salt extracted meat protein might intensify the network ofmeat proteins and hence produced a uniform meat matrix with improved structural strength andstability. These results were similar to those of other food hydrocolloids, such as starch, konjacglucomannan, and hydroxypropyl methylcellulose mixed with SSP in restructured seafood.[38–39]

Texture profile analysis

The different attributes of texture profile of different meat emulsion samples are presented in Table 3.The hardness values at day zero differed significantly (P < 0.05) among different samples, and it wasobserved highest in the control samples. Thus, incorporation of AG in the meat emulsion formulationhad resulted in the reduction of hardness values. This was in agreement with dynamic rheologicalvalues (G’ and G’’) which also suggested less elastic behaviour of meat emulsion samples containingAG as compared to the other samples. The addition of AG with VO also resulted in lower chewinessvalues (P < 0.05) than control samples. However, chewiness at day zero was non-significant betweenAGT1, VOT2, and AGVOT3 samples. The values for chewiness increased gradually from day zero today eight in all samples irrespective of treatment. The increment in chewiness values was observedmore in AG-treated samples. Somewhat similar trends were observed for gumminess values at day zeroand subsequent storage period.

Similar hardness and chewiness trends were observed for low-fat salami containing rice bran oil andmalva nut gum[5]; for meat emulsion containing sodium stearoyl-2-lactylate and carrageenan[37]; and forfrankfurters containing canola-olive oil, rice bran, and walnut.[40] The softening of the product’s texturewas also observed when plant oil was used for manufacturing of low-fat meat products.[41]

Marchetti et al.[26] used various binders with fish oil to formulate low-fat meat emulsions, and theyconcluded that fish oil reduced around 40.2% of hardness than the control samples. Addition of fish oilresulted in lower hardness value in these experiments. In our previous experiments,[14] it was concludedthat AG addition resulted in more water binding and fat binding properties of low-fat meat emulsion. Thismight be the reason behind lower hardness and chewiness values of meat emulsion samples containingAG.During storage period, the hardness values increased in all groups, and the increase was observed more inAG-treated samples. This might be due to more water content (more evapouration and dryness duringstorage) in the AG-containing samples because of high water holding capacity.[14]

The springiness values also differed significantly (P < 0.05) among different samples initially.Lowest springiness values were obtained for control samples. No definite trend was observed duringstorage period for springiness values. In most instances, springiness values did not change (P < 0.05)

(a) (b)

Figure 3. Scanning electron microscopic (SEM) images of full-fat meat emulsion (VOT2) samples: (a) at 500×, (b) at 1000×.

S1138 Y. KUMAR ET AL.

Table3.

Effect

ofaloe

gel(AG

)additio

non

texturalattributes

(texture

profile

analysis,TPA

)of

cooked

meatem

ulsion

durin

grefrigerated

storage(m

ean±SD

)(n

=9).

Storageperio

d(Days)

Attributes

Samples

02

46

8

Hardn

ess

AGT1

45.10±0.40

cD53.77±2.82

aB48.49±0.48

bC

56.62±0.63

aA56.02±0.01

aA

VOT2

49.57±2.91

bB

51.49±0.23

abB

54.84±0.89

aA55.45±0.28

bA

55.48±0.31

bA

AGVO

T345.44±3.31

cC49.48±1.03

bB

52.42±4.12

abA

48.85±1.34

dB

49.07±0.48

dB

CT4

54.24±3.02

aB53.01±4.85

abB

57.49±7.80

aA53.33±0.81

cB52.82±0.27

cC

Sprin

giness

AGT1

0.83

±0.01

cB0.82

±0.02

abC

0.85

±0.03

aA0.83

±0.01

bC

0.83

±0.01

bC

VOT2

0.87

±0.01

aA0.81

±0.01

bB

0.82

±0.02

bB

0.82

±0.01

cB0.82

±0.01

cB

AGVO

T30.84

±0.01

b0.84

±0.03

a0.84

±0.01

ab0.84

±0.01

a0.84

±0.02

a

CT4

0.83

±0.02

bc

0.84

±0.01

a0.82

±0.01

b0.83

±0.01

ab0.83

±0.01

Cohesiveness

AGT1

0.65

±0.02

B0.62

±0.02

C0.67

±0.04

aA0.64

±0.02

cB0.65

±0.02

bB

VOT2

0.61

±0.03

B0.62

±0.02

B0.62

±0.02

bB

0.65

±0.01

bcA

0.66

±0.01

bA

AGVO

T30.65

±0.03

B0.64

±0.01

C0.66

±0.01

abB

0.68

±0.02

aA0.69

±0.02

aA

CT4

0.65

±0.03

AB

0.63

±0.03

BC

0.64

±0.04ab

B0.66

±0.01

bA

0.65

±0.01

bAB

Chew

iness

AGT1

25.31±1.05

bC

27.40±1.30

aB27.77±2.36

bB

30.00±0.44

aA30.11±0.90

bA

VOT2

26.36±1.79

bC

25.63±1.02

bD

28.14±0.25

abB

29.55±0.71

abA

29.99±0.44

bA

AGVO

T324.71±1.95

bD

26.61±0.49

abC

28.86±1.45

abB

27.78±0.23

cB33.43±4.79

aA

CT4

29.22±3.42

aA27.83±1.66

aB30.12±2.30

aA29.31±0.44

bA

28.62±0.55

bAB

Gum

miness

AGT1

30.53±1.03

bC

33.25±1.82

B32.52±1.58

bB

36.19±0.79

aA36.34±1.36

bA

VOT2

30.44±2.09

bD

31.78±1.27

D34.20±0.32

bC

36.17±0.57

aB38.17±1.35

aA

AGVO

T329.35±2.52

bB

31.71±0.77

B34.36±1.99

abA

33.04±0.01

cA33.88±0.63

cA

CT4

35.12±3.39

a33.21±2.28

36.61±2.80

a35.12±0.53

b34.30±0.66

c

Forsampledeno

mination,

seeTable1.

Meanvalues

with

common

smalllettersuperscript(treatmenteffect)in

acolumnforeach

attributedidno

tdiffe

rsign

ificantly(P

<0.05).

Meanvalues

with

common

capitallettersuperscript(storage

effect)in

arow

didno

tdiffe

rsign

ificantly(P

<0.05).

INTERNATIONAL JOURNAL OF FOOD PROPERTIES S1139

during whole storage period in any of the samples. The cohesiveness values at day zero and day twodid not differ significantly (P < 0.05). The cohesiveness gradually increased during storage period inall the treatments and differed significantly.

Microstructure

The scanning electron microscopic (SEM) images of the full-fat (VOT2) and low-fat raw meat emulsion(AGVOT3) at different magnifications are shown in Figs. 3a and 3b, and 4a and 4b, respectively. Themicrostructure of VOT2 showedmore cracks with oil droplets of irregular shapes and size in comparisonwith AGVOT3 samples. The AGVOT3 samples showed more regular, compact, and dense continuousphase as compared to VOT2 samples.

Addition of AG had provided more stability[14] to the salt extracted meat proteins which might bethe cause for a homogenous network in AGVOT3 samples. The results of textural properties were alsoin agreement with the properties of SEM micrographs and with the dynamic rheological properties ofdifferent emulsion samples. This could be attributed to the reaction between AG polysaccharides andmuscle protein–water phase.

Similarly, Jiménez-Colmenero et al.[42] studied pork fat replacement with an emulsified olive oil infrankfurters and found smaller cavities and a firmer network than the control samples. Jiménez-Colmeneroet al.[43] also described changes in the structure of reduced-fat frankfurter when KG was added in theformulations. Similar findings on the microstructure have also been reported by Salcedo-Sandoval et al.(2013) when some fat replacers have been used during manufacturing of low-fat meat products.

The formation, properties, and stability of meat emulsion depend predominantly on protein and thepresence of other non-meat ingredients in the mixture. Moreover, efficient formation of fat globules is aprerequisite for well-stabilised emulsion structure.[44] In the present study, microstructural imagesrevealed that AG-VO-fat globules reduced the porosity and significantly increased the stability ofemulsion which suggested that AG might enhance the emulsifying ability of meat proteins. In most ofthe previous studies, the fat of animal origin or combinations of animal and vegetable fat were used. It iswell established that the type of fat affects the distribution of fat and influences the meat emulsionstability. Substitution of animal fat (high melting point) with vegetable oil (low melting point) facilitatesuniform distribution of oil droplets in meat emulsion which leads to more stabilised and homogeneousprotein–water–fat matrix. In the present study, the AG and VO combination improved the emulsifyingability of meat proteins as well as stabilised oil droplets more efficiently which might be due to theformation of thin protein film around the fat droplets (Fig. 5) or by establishing some other adhesionforces (previous section results; G’ and G’’) between protein, water, and fat molecules (Fig. 5).

(a) (b)

Figure 4. Scanning electron microscopic (SEM) images of low-fat meat emulsion (AGVOT3; 50% fat replacement) samples: (a) at500×, (b) at 1000×.

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Oxidative stability

Nature of the product, type of muscles, amount and type of fats, and the presence of antioxidants affect theoverall oxidative stability of meat products. TBARs estimation is the method which suggests the stability ofa food system against oxidation chain reactions.[45] The changes in the TBARs values of different samplesduring eight-day refrigerated storage period are shown in Fig. 6. TBARS values were significantly affected(P < 0.05) by ingredient combination and storage duration. In general, the higher oxidative stability wasobserved (low TBARs) (P < 0.05) in samples containing AG. VOT2 samples showed highest TBARs value.This might be due to more fat content of VOT2 samples. Similarly, Estévez et al.[46] reported significantly

Figure 5. Scanning electron microscopic (SEM) image of low-fat meat emulsion (AGVOT3; 50% fat replacement) samples at 2500×.The arrows suggest possible adhesion between protein, water, and fat molecules and formation of thin film around the oildroplets.

Figure 6. TBARs (mg malonaldehyde/kg) values of different meat emulsion samples during refrigerated (4 ± 1°C) storage (n = 9).For sample denomination, see Table 1.

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higher levels of TBARs in high-fat meat products. The presence of antioxidants in AG[47] might be anotherreason behind lesser TBARs value in samples containing AG. Likewise, konjac addition in the reformulatedmeat products also led to lower TBARS values when added to total pork back fat replacement samples.[48]

The vegetable (plant) oil contains more mono and polyunsaturated fatty acids as compared toanimal fat (more saturated fatty acids). The polyunsaturated fatty acids are more prone to oxidativedamage due to the presence of less stable multiple bonds.[48] These bonds are easily attacked by somepro-oxidants and reactive oxygen species. This favours the oxidative chain reactions to occur. MoreTBARs in VOT2 samples in present study were due to this reason. In the earlier studies, it wasconfirmed that meat products containing plant oil or more unsaturated fatty acids had lesser oxidativestability.[4,49]

Conclusion

The effect of aloe gel on the rheological parameters of meat emulsion was evaluated. The addition of AGin themeat emulsion formulation improved the emulsifying ability ofmeat proteins and resulted inmoreuniform emulsion matrix than other samples as suggested by the mechanical spectra, SEM, texturalstudies, and modelling of rheological parameters according to the power law equations. Addition of aloegel also resulted in higher oxidative stability of low-fat meat emulsion samples. Thus, low-fat meatproducts may be made with the addition of aloe gel during manufacturing of emulsion-type meatproducts.

Funding

The authors would like to extend thanks to Indian Council of Agricultural Research, India for financial support to thisresearch project (Grant number: IXX12120, Institute Project).

ORCID

Yogesh Kumar http://orcid.org/0000-0002-2688-5893

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