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Effect of Processing Conditions and Raw Materials on the Properties of Kishk 2. Sensory Profile and Microstructure
Lebensm.-Wiss. u.-Technol., 33, 452}461 (2000)
E!ect of Processing Conditions and Raw Materials on the Properties of Kishk 2. Sensory Pro"le and Microstructure D. D. Muir, A. Y. Tamime* and M. Khaskheli
D. D. Muir: Hannah Research Institute, Ayr KA6 5HL (Scotland) A. Y. Tamime, M. Khaskheli: SAC Auchincruive, Food Systems Division, Ayr KA6 5HW (Scotland) (Received March 14, 2000; accepted June 14, 2000)
Diwerences in sensory character of Kishk were associated with cereal type and dairy base. When oat products were used as the cereal component, the Kishks were similar, but products made from Burghol and wheat your diwered in mouth-feel. In addition, the Kishks made with Burghol or Burghol your were easily distinguished from products made from wheat your. The length of the *conditioning+ period only inyuenced the *acid+ character of Kishk made with a combination of Burghol and low-fat yoghurt. The starch content in the yoghurt/Burghol or wheat your mixture decreased linearly during the *conditioning+ period as a result of a-amylase activity. The microstructure of the Kishk doughs was consistent with the normal pattern of degradation of wheat starch in which much of the original granular structure is retained during the *conditioning+ period.
2000 Academic Press Keywords: Kishk; sensory attributes (aroma, #avour, aftertaste, mouth-feel); cereals; acidulants; &conditioning' period; microstructure
Introduction Most Kishk products are made from di!erent cereal products and fermented milk base by traditional methods of manufacture (1, 2). The sensory properties of Lebanese Kishk reconstituted with water and served as a hot porridge or gruel have been pro"led by Muir et al. (3). The product made with caprine milk was clearly distinguishable from the rest of the Kishk samples. Tamime et al. (4) found that the mouth-feel attributes (&grainy', &sticky' and &slimy' character) of Kishk were associated with the type of Burghol used (e.g. wheat, barley or oats). In contrast, much less is known of the e!ect of modifying the properties of the milk base (unfermented, chemically acidi"ed with D-glucono-d-lactone (GDL) and yoghurt), but the properties of these Kishks have been described elsewhere (5). In contrast to Burghol, #our is a fractionated whole grain. That is, the starchy endosperm is selectively separated from the bran and germ, then milled into smaller particles; thus increasing the accessibility to enzymolysis (6). During the &conditioning' period of Kishk-making (1), the cereal enzymes have the potential to degrade the * To whom correspondence should be addressed. Present address: 24 Queens Terrace, Ayr KA7 1DX (Scotland).
0023-6438/00/060452#10 $35.00/0 2000 Academic Press
carbohydrate and protein. In addition, further acid development by the starter culture could in#uence the quality of Kishk. No data has been reported on the role of the &conditioning' period in Kishk-making, but recently, some researchers (7, 8, 9) have studied the e!ect of di!erent ingredients (e.g. fresh onions, tomato puree, salt, baker's yeast and powder consisting of a mixture of paprika, dill and mint) on the &conditioning' period activity, and the kinetics of operating variables on starch gelatinization during extrusion of Trahan (Greek or Turkish Kishk) made with wheat #our and full-fat yoghurt. The objectives of this paper were: (a) to determine the e!ect of milk components in combination with a range of di!erent cereal types on the sensory properties of Kishks; (b) to study the e!ect of di!erent treatment of the cereals on the sensory character of Kishk; (c) to evaluate changes in the sensory pro"le of Kishk produced using di!erent &conditioning' periods; and (d) to investigate changes in the structure of cereal starch during the &conditioning' period.
Materials and Methods Manufacture of Kishk Three sets of Kishk samples (A, B and C) were produced by the same method described in an earlier study (5).
doi:10.1006/ fstl.2000.0687 All articles available online at http://www.idealibrary.com on
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Sensory proxling Sensory pro"ling was carried out using a protocol successfully applied to a diverse range of commercial samples (3). Initially, the panel of assessors and the sensory scientists agreed on lists of descriptors for the modalities: odour, #avour, aftertaste and mouth-feel. The panel were acclimatized to the sensory properties of Kishk using commercial samples. The attribute ratings were tested for ability to discriminate and redundant or poorly understood terms were deleted from, the additional descriptors inserted into, the experimental vocabulary. The "nal vocabulary, derived for commercial products, was applied without modi"cation to the laboratory-prepared Kishk in the present study. The pro"le comprised seven attributes to describe aroma (&overall intensity', &creamy/milky', &acid/vinegary/sharp', &fruity/sweet', &cooked', &cereal', &cardboard'), ten #avour attributes (&overall intensity', &creamy/milky', &acid/vinegary/sharp', &fruity/sweet', &cooked', &cereal', &cardboard', &apple', &bitter', &salty'), "ve descriptors of aftertaste (&overall intensity', &persistence', &acid/vinegary/sharp', &cereal', &cardboard'), and "ve terms used to describe mouth-feel (&viscosity', &grainy/#oury/chalky', &sticky/gluey', &slimy', &mouth-coating'). Assessors The panel of assessors was an external panel of 15 female nonsmokers, aged 39}55, whose sole duties were sensory characterization. The panel were selected on the basis of sensory acuity and consistency and are highly experienced in pro"ling a wide range of foods. Panel performance is assessed by the principles described by Hunter et al. (10). Sample preparation Kishk samples made from di!erent cereal types and dairy bases were treated in an identical fashion. Each dried powder was mixed with four parts cold tap water and brought to boiling point with continuous stirring. After simmering for 5 min with occasional stirring, the product was immediately served hot in ceramic cereal bowls. Sample presentation Sample assessment was carried out in isolated air-conditioned booths with controlled lighting. Assessors cleansed their palate with a plain, water biscuit and some cold water then rated each sample for the attributes listed above. Two samples were presented in each tasting session, and several sessions, i.e. four to six, were held on each day. The order of the presentation of samples was balanced (11). Rating of attributes was on an undi!erentiated scale with anchor points (absent, extremely strong) and was facilitated by an interactive, computer-assisted data collection system (12). Samples were pro"led twice. Data analysis Mean sample e!ects were computed by analysis of variance (ANOVA) and principal components analysis as
Table 1 Experimental treatments and levels Treatment Base type Cereal Inhibitor Test time Supplier
Levels Yoghurt; whey from yoghurt Burghol; wheat #our Sodium azide, antimicrobial tablets Fresh; 2, 4 and 6 days Two di!erent sources
detailed by Muir et al. (3). To further simplify interpretation of the sensory space maps, Factor Rotation (varimax) was applied to the Principal Component Analysis (PCA).
*Conditioning+ period To assess the role of the enzymatic hydrolysis (microbial and a-amylase activity) of the macronutrients of the dough during the &conditioning' period, an experiment was conducted to observe the possible enzymatic e!ects as well as the structural changes. The experimental treatments and levels constituted a randomized complete block design replicated one time with repeated measurements at four time-points. The treatment had a factorial structure shown in Table 1. Sodium azide (Fisher Scienti"c Ltd., U.K.) was added at a rate of 0.2 g/kg to inhibit the growth of microorganisms including the starter culture (13). The bacterial activity was monitored by measuring the soluble nitrogen content in the dough which is similar, in principle, to the maturity index in cheese; however, sodium azide is a hazardous chemical leading to explosion at high temperatures which makes the test for soluble nitrogen very dangerous. Parallel samples were used where the sodium azide was replaced with antimicrobial tablets (50 tablets/kg dough; Broad Spectrum Microtab] II, D and F Control Systems Inc., U.S.A.). The soluble nitrogen content, a-amylase activity and starch content were determined according to the method described by IDF (14) and Anonymous (15, 16), respectively.
Microscopic analysis A Laser Scanning Confocal Microscope (LSCM) MRC1000 (Bio-Rad Microxience Ltd., U.K.) was used to study the microstructure of the dough during the &conditioning' period. The samples were "xed in a 25 g/kg aqueous glutaraldehyde solution (TAAB Laboratories Equipment Ltd., U.K.) as described by Lewis (17), Tamime et al. (18) and Kalab (19), washed with distilled water, dehydrated in graded ethanol (700, 800, 900, 1000 g/kg) and embedded in LR white acrylic resin (London Resin Company Ltd., U.K.). The embedded samples were sectioned using an UB Ultratone (type 8801A; LKB-Producter A/B, Sweden) and stained with Acridine Orange (1 g/kg; Sigma Company Ltd., U.K.). The images were recorded and stored on the hard disc of the computing system connected to the microscope.
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Table 2 E!ect of di!erent cereal type and dairy base on the sensory ratings of Kishk (set A) Treatment e!ect (0}100) Porridge oats Attribute Odour Intensity Creamy Acid Fruity/sweet Cooked Cereal Cardboard Flavour Intensity Creamy Acid Fruity/sweet Cooked Cereal Cardboard Apple Bitter Salty Aftertaste Intensity Acid Cereal Cardboard Mouth-feel Viscosity Chalky Sticky Slimy Mouth-coating
Oat #our
Burghol
Wheat #our
M?
GDL@
YA
M
GDL
Y
M
GDL
Y
M
GDL
Y
SEDB
47.5 30.6 5.7 28.1 42.4 36.3 18.4
48.8 14.3 29.8 16.2 42.1 34.8 14.0
43.4 19.2 22.6 18.6 38.4 33.0 10.0
50.3 34.2 2.7 30.5 43.5 40.9 17.4
44.5 12.0 27.7 13.0 37.7 32.9 15.7
37.6 12.9 19.8 16.9 32.1 25.8 9.3
47.7 25.5 9.8 29.2 38.0 38.0 10.5
46.5 14.1 26.5 17.8 40.7 35.9 11.7
41.8 17.3 18.9 18.4 34.0 34.9 11.5
47.0 26.0 10.1 25.1 40.8 33.6 12.6
47.2 11.5 33.0 16.5 39.3 26.0 10.5
46.1 11.5 31.0 14.7 34.0 17.8 15.3
3.92 3.35 4.83 3.49 3.92 3.63 3.28
48.5 31.4 10.8 27.1 46.4 42.0 28.3 4.3 3.0 7.1
53.9 21.0 40.4 16.9 44.5 37.6 16.2 10.1 9.9 16.8
57.6 19.3 48.3 20.1 43.2 35.4 18.8 8.0 11.3 17.5
43.1 30.6 4.8 25.4 46.1 38.5 27.6 0.5 1.4 1.8
52.8 18.0 43.2 18.1 40.7 36.3 21.0 8.1 6.9 18.4
58.1 21.5 56.2 25.2 38.8 34.4 20.0 11.6 9.5 21.5
48.9 28.0 14.5 28.0 39.2 48.6 19.7 2.3 2.6 6.6
53.3 24.3 32.9 28.1 40.8 45.8 11.0 6.6 5.1 19.2
57.7 18.8 44.9 26.2 35.5 41.9 14.2 13.8 9.1 20.9
48.1 30.7 10.1 35.5 44.9 33.8 21.4 3.4 4.8 6.7
50.7 18.5 52.3 23.9 42.2 29.1 23.0 7.3 11.8 19.9
61.0 17.2 60.2 21.4 37.4 26.6 22.0 6.9 16.8 23.5
4.34 3.31 5.88 3.56 3.69 3.50 3.67 2.41 2.33 3.31
40.8 8.3 35.0 23.4
42.0 30.4 33.0 12.5
43.5 36.7 30.1 12.2
38.0 2.8 35.4 21.7
43.4 33.7 31.3 20.5
48.0 43.5 27.4 15.8
42.9 8.7 37.1 12.3
42.0 24.9 37.3 9.7
45.8 40.6 31.7 13.0
39.5 7.3 29.2 22.2
51.6 44.9 25.3 15.7
58.4 51.6 21.1 16.9
2.66 4.36 3.21 3.50
69.4 33.3 56.6 23.0 45.8
71.3 29.0 64.0 30.1 48.7
66.5 31.6 65.4 29.8 49.8
67.5 39.7 52.8 16.4 47.8
65.5 27.6 58.3 29.4 47.9
63.1 24.4 57.4 29.0 47.1
67.9 56.0 20.7 2.7 40.6
64.4 56.7 22.4 3.5 37.9
65.7 54.9 25.7 4.2 42.2
65.4 21.8 67.2 52.3 46.6
66.8 17.3 74.1 64.2 49.9
66.5 20.0 76.2 70.3 54.5
4.86 4.04 3.34 4.71 3.66
? Unfermented milk. @ D-Glucono-d-lactone. A Yoghurt. B Standard error of di!erence of mean.
Results and Discussion Gross chemical composition of Kishk The average chemical composition of Kishk samples (sets A, B and C) were reported by Tamime et al. (5). The di!erences between samples were mainly associated with cereal type and processing conditions; however, the chemical composition of the experimental Kishks were within the range of commercial Kishk samples sold in the Lebanese market (20). Sensory properties~The ewect of dairy base and cereal type Kishks (set A) The di!erences in the sensory quality of the Kishk was mainly associated with the type of dairy base used (Table 2). For example, the product made with unfermented milk was much more &creamy', &fruity/sweet', &intensity' (odour and #avour), &cereal', &cardboard' (odour #avour and aftertaste), less &acid' (odour, #avour and aftertaste), and &salty', &apple', &bitter' (#avour) to the corresponding products made with yoghurt. The GDLbased Kishk had slightly higher scores for &cereal' (odour,
#avour and aftertaste), &cooked' (odour and #avour) and &acid' (odour), but less for &creamy' (odour), &acid' (#avour and aftertaste), and &bitter', &salty' (#avour) when compared with Kishk made with yoghurt. Thus, the type of acidulant (i.e. GDL vs. yoghurt) also a!ected the sensory pro"le of the product. The mouth-feel attribute of Kishk made with unfermented milk was perceived as slightly more &viscous' and &chalky', but less &sticky', &slimy' and &mouth-coating'. Although the Kishk made with GDL or yoghurt had similar mouth-feel ratings, the latter product was perceived to be more &sticky', &mouth-coating' and &slimy'; these characters were in#uenced by the cereal type used. There was no evidence of systematic di!erences in odour, #avour, (except &fruity/sweet') or aftertaste (except &intensity') being associated with cereal type. While appreciable di!erences were found between mouth-feel characters (&chalky', &sticky', &slimy') these attributes were associated with the cereal type. Principal component analyses (PCA) (with Factor Rotation : varimax) were used to simplify interpretation of the main di!erences between products. Factor 1 explained 31% of variance and Factor 2 a further 25%. For
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Fig. 1 Sensory space maps based on Factor scores after PCA for Kishk (set A) made with di!erent cereals and milk bases. 䊏 䊐 Unfermented Milk; 䊉 䊊 GDL; 䉱 䉭 yoghurt. Closed symbols represent rolled oats or Burghol. Open symbols represent oat or wheat #our
Fig. 2 Star plots for the e!ect of cereal type on perceived mouth-feel attribute of Kishk (set A). A and B are di!erent sources of oats and wheat products
convenience, the mean scores for each of the 12 combinations of cereal and dairy base were used to construct separate sensory space maps for oat- and wheat-based products. Factor 1 was associated with cereal type, and Factor 2 with dairy base. For oat-based products, there was a clear progression on Factor 2 from unfermented milk through GDL-acidi"ed milk to yoghurt-based product (Fig. 1*oat). There is no evidence of a signi"cant di!erence between Kishk made from rolled oats or oat #our (Factor 1). The separation of Kishk on Factor 2 was associated with di!erences in #avour intensity * in particular, &acidic', &bitter', and &salty' character (data not shown). In wheat-based Kishk, a di!erent picture emerged (Fig. 1*wheat). Here, the products were clearly separated in terms of particle size by the scores on Factor 1. The
Kishk made from wheat #our was distinguished by its &sticky' and &slimy' character (ratings were 67}76 and 52}70, respectively), and that from Burghol by its &chalky' nature (55}57; see Table 2). On the other hand, separation on Factor 2 was essentially the same as that observed for all oat products, i.e. there was a progression from unfermented milk to yoghurt in terms of #avour &intensity'. To aid comparison of the e!ect of the cereal type on the perceived mouth-feel character of Kishk, a star plot was constructed (Fig. 2). Each attribute is assigned a vector, the length of which is determined by the magnitude of the attribute, expressed as a proportion of the maximum value within the sample set. The major variations in attributes were in &chalky', &slimy' and &sticky' characters. Variation between the plots for the Kishks based on oat
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Fig. 3 Sensory space maps based on Factor scores after PCA of Kishk (set B) made with di!erent wheat products. Unfermented milk GDL Yoghurt Burghol 䊏 䊉 䉱 Burghol #our 䊏 䊉 䉱 Wheat #our 䊐 䊊 䉭 (a) and corresponding vector loading for Factors 1 and 2. 䊏 Mouth-feel, 䉱 aftertaste, 䊉 #avour (b)
were minor. In contrast, the plots for Burghol and wheat #our demonstrated a clear di!erence. Burghol-based Kishk contrasted quite di!erently to those made from wheat #our indicating the in#uence of the particle size of cereals and method of preparation, i.e. parboiled cracked wheat vs. wheat #our. There were clear indications from Figs. 1 and 2 that the e!ect of cereal particle size (irrespective of the dairy base) was important. The e!ect of treatment (i.e. cereal type, dairy base and particle size) on the sensory attributes was examined by ANOVA, and the signi"cant treatment effects (data not shown) could be summarized as follows: (a) cereal type had only e!ect on &fruit/sweet' (#avour) (P(0.01), and &intensity' (aftertaste), &chalky', &sticky' and &slimy' (mouth-feel) (P(0.001); (b) the dairy base had the greatest e!ect on sensory characters (P(0.001) with the exception of &cardboard' (odour), &cooked' and &cardboard' (#avour), and &viscosity', &chalky' and &mouthcoating' (mouth-feel); and (c) the di!erences between the cereals supplied by di!erent sources was limited to changes in &intensity', &cooked' (odour) and &slimy' (mouth-feel) (P(0.001); &cooked', &cardboard' (#avour) and &chalky' (mouth-feel) (P(0.01), and &acid' (odour) (P(0.05). The e!ect of cereal particle size was particularly important for mouth-feel characters [&chalky', &sticky', &slimy' (P(0.001)], &mouth-coating' (P(0.01), and aftertaste [&cereal' (P(0.001), &intensity', &acid' and &cardboard' (P(0.01)]. The interaction of the cereal type;dairy base was only signi"cant (P(0.05) for &cardboard' (odour) and &fruity/sweet' (#avour), whilst the dairy base;cereal particle size interaction was only signi"cant for #avour attributes &apple' (P(0.01) and &fruity/sweet' (P(0.05). The cereal type;particle size interaction was highly signi"cant for mouth-feel (&chalky', &sticky', &slimy' and &mouth-coating'; P(0.001), and for #avour (&cereal',
&apple' and &bitter'; P(0.001); on odour and aftertaste (&cereal'; P(0.01 and &acid', P(0.05) and for aftertaste (&intensity'; P(0.05). The dairy base;size of the cereal interaction was only signi"cant on &intensity' (aftertaste; P(0.001), &cereal' (odour; P(0.01) and &acid' (#avour and aftertaste; P(0.01).
Sensory properties~The ewect of particle size of wheat-based Kishks (set B) The sensory rating for the Kishks made with Burghol or Burghol #our were very similar, but di!erent from samples made with wheat #our; the results are wholly consistent with those reported for Kishk samples (set A) (data not shown; see Table 2). Once again PCA (with Factor Rotation) was used to simplify interpretation of di!erent products. Two Factors explained 35.3 and 30.8% of variance, respectively. In this instance, the Kishk samples were separated in the "rst Factor in terms of dairy base (Fig. 3a) while Factor 2 was associated with di!erences in particle size. As had been observed previously with sample set A, the progression from unfermented milk to yoghurt was associated with an increase in #avour &intensity', particularly with &acidic', &bitter', &salty', and &cereal' notes (Fig. 3b). In addition, separation on Factor 2 was associated with &chalky' mouth-feel for Burghol with a transition to &sticky' and &slimy' character for wheat #our. Burghol #our was only slightly separated from Burghol. The di!erences in sensory character were not simply related to particle size because wheat #our was di!erent from Burghol #our. On the other hand, the di!erences between Burghol and Burghol #our were modest. These results suggest that the di!erences between products are associated with the production method used to produce Burghol, not with particle size per se (1).
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Table 3 Signi"cant changes in ratings of sensory attributes (0}100) during the &conditioning' period of the Kishk dough (set C) Length of the secondary fermentation (days) Attribute Odour Intensity Creamy Acid Fruity/sweet Flavour Intensity Creamy Apple Acid Salty Aftertaste Intensity Acid Persistence
0
2
4
6
SED?
36.2 13.0 5.1 18.5
36.3 14.6 4.7 15.9
36.6 7.7 13.8 13.2
41.9 8.8 19.6 14.4
2.01 2.14 2.44 1.52
50.6 19.1 2.5 27.3 21.9
53.7 19.8 7.9 43.4 30.0
59.9 18.3 8.6 53.7 34.4
64.5 9.8 9.1 60.3 36.8
1.69 4.43 1.60 5.00 3.03
41.4 14.2 38.6
45.7 36.3 45.5
50.7 42.6 48.0
53.7 47.1 52.8
2.25 2.82 2.44
Fig. 4 a-amylase activity (units/g) of wheat cereals/yoghurt mixture (set C) during the &conditioning' period. 䊉 Burghol# yoghurt; 䊊 Burghol#yoghurt#sodium azide; 䉱 Wheat #our#yoghurt; 䉭 Wheat #our#yoghurt#sodium azide
? Standard error of di!erence of mean.
Sensory character~The ewect of *conditioning+ period on Kishk (set C) The changes in sensory pro"les as a function of the length of the &conditioning' period were investigated by pro"ling the Kishk dough when fresh (0 days), and at 2, 4 and 6 days (control). No signi"cant treatment e!ects were observed for &cooked', &cereal' or &cardboard' odour; for &fruity', &cooked', &cereal', &cardboard' or &bitter' #avour; or for &viscous', &grainy', &slimy', &sticky' or &mouth-coating' aspects of mouth-feel. However, there were signi"cant e!ects associated with the attributes shown in Table 3. The pattern of change di!ered between attributes. The most marked changes were associated with &acid' character for odour, #avour and aftertaste. There tended to be a greater change in the end of the &conditioning' period than at the start. Odour and #avour &intensity' and the &intensity' of aftertaste and its persistence followed a similar pattern (Table 3). On the other hand, &creamy' odour and #avour, and &fruity' odour declined during the &conditioning' period. &Apple' #avour receded, albeit from a low base, over the period studied. Although there was no evidence from chemical analysis of changes in salt content the perception of saltiness increased during the &conditioning' period. The main changes were in &acid' character, and these corresponded to growth of the yoghurt micro#ora during the &conditioning' period (5).
Amylase activity (set C) The a-amylase activity during the &conditioning' period is shown in Fig. 4. This enzyme activity (units/g) was detected in yoghurt, Burghol and wheat #our at 0.019, 0.012 and 0.046}0.069, respectively (21; data not shown). The presence of this enzyme in ¸actobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus has never been reported previously, but has recently been
noted in many strains of lactobacilli isolated from Nigerian fermented foods (22). However, protein fractions precipitated from whey, concentrated milk or serum contained a-amylase activity (23}27), therefore, such as enzyme could then be present in yoghurt. A range of a-amylase activity in wheat #our supplied from di!erent sources was evident (21), and this could be due to factors such as growing, harvesting or milling (28). The a-amylase activity increased slightly in wheat #our-based yoghurt mixtures on the second day of the &conditioning' period and then decreased (Fig. 4). In contrast, in Burghol-based mixtures the a-amylase activity increased progressively and sharply after 4 days until the end of the &conditioning' period. This is probably due to the destruction of a-amylase activity between the pericaptesta and endosperm-germ fractions (29). During the re"ning of #our, a-amylase activity is lost. However, in the presence of moisture originating from yoghurt, the cereal tends to swell or becomes soft encouraging the release of a-amylase into the yoghurt/Burghol mixture (30). The changes in a-amylase activity in the wheat #our/ yoghurt mixture were comparatively small and unlikely to be of practical signi"cance (28, 30}32), and the presence of sodium azide did not cause any inhibition to a-amylase (see Fig. 4). The signi"cance of treatment e!ects were cereal type (P(0.01), &conditioning' period (CP) and cereal type;CP (P(0.001), and yoghurt;CP (P(0.05).
Starch (set C) The starch content in all the cereal/yoghurt mixtures including the samples containing sodium azide were reduced by ca. 40% at the end of the secondary fermentation state (Fig. 5). The reduction in the starch content in all the samples was similar and relatively linear. Analysis of variance showed that signi"cant di!erences for CP (P(0.001), cereal type;CP (P(0.01) and yoghurt;CP (P(0.05).
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Fig. 7 Microstructure of starchy endosperm of yoghurt/Burghol mixture (set C) during the &conditioning' period when fresh; arrow illustrate starch granules
Fig. 5 Decrease in starch content (expressed as %) of yoghurt/wheat cereals mixtures (set C) during the &conditioning' period. 䊉 Burghol#yoghurt; 䊊 Burghol#yoghurt# sodium azide; 䉱 Wheat #our#yoghurt; 䉭 Wheat #our# yoghurt#sodium azide
Fig. 6 Soluble nitrogen content (g/kg) of wheat cereal/yoghurt mixtures (set C) during the &conditioning' period. 䊉 Burghol#yoghurt; 䊊 Burghol#yoghurt#sodium azide; 䉱 Wheat #our#yoghurt; 䉭 Wheat #our#yoghurt#sodium azide
Soluble nitrogen (set C) The pro"le of increase of soluble nitrogen content in the cereal type/yoghurt mixtures during the &conditioning' period is shown in Fig. 6. This re#ects primarily the metabolic activity of microorganisms of the protein which is similar to the maturity index of cheese during the storage period (5, 26). No signi"cant increase in the soluble nitrogen content was evident in Burghol-based mixtures, whilst in #our-based products a sharp increase was obtained. This could be attributed to the availability of protein for hydrolysis in wheat #our as compared to the more protective starch cellular structure of Burghol. Also, the particle size of the cereal may have played
a contributory role a!ecting the rate of protein hydrolysis. The addition of antimicrobial tablets to the mixture, in part, controlled the microbial activity, and a lower amount of soluble nitrogen was produced (see Fig. 6). Furthermore, the yoghurt micro#ora, yeasts or moulds were not recovered from any of the dough mixtures (up to 6 days) within the sensitivity of the test (i.e. 10\ dilution) for all the samples containing sodium azide which has a bactericidal e!ect against Gram-positive bacteria; however, sodium azide controlled, in part, certain species of nonactic acid bacteria (13, 21). Analysis of variance of treatment e!ects were signi"cant (P(0.01) for cereal type, CP, cereal type;CP and cereal type;CP yoghurt.
Microstructure of the Kishk dough (set C) Confocal scanning laser microscopy (CSLM) revealed information on the "ne structure of Kishk and its constituents, but the relatively large particle size and uneven distribution of the constituents makes obtaining a single overall view of the structure di$cult (33). However, selected structural entities can be identi"ed at all stages of the &conditioning' period and the changes during processing can be deduced. The structural entities selected were the cereal endosperm tissue, the &free' yoghurt regions, and the interphase between the two. The starchy endosperm of yoghurt/Burghol mixture when fresh are shown in Fig. 7. The starch consisted of a population of granules which were essentially oval in shape. Some granules retained the lenticular forms of type A wheat starch, but others were swollen and deformed. The deformation was possibly in#uenced by the manufacturing stages of Burghol where the grains were steeped in boiling water, dried to its original moisture content, rehydrated with ca. 200 g/kg moisture, cracked and dried (1). Similar microstructural changes in wheat starch dispersions during heating and cooling have been reported by Langton and Hermansson (34). The microstructure of starch granules at the end of the &conditioning' period were more irregular in shape, swollen and tended to stick together; even when sodium azide was added to the mixture to control the microbial
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Fig. 8 Starchy endosperm structure of whey/Burghol mixture when fresh (a) and after six days (b) during the &conditioning' period; arrows illustrate starch granules
Fig. 9 Microstructure of starch granules in yoghurt/wheat #our mixture (set C) during the &conditioning' period [fresh (a) and after six days (b)]; arrows show starch granules and white specks illustrate protein aggregates
activity, no di!erence(s) was observed in the behaviour of the starch granules (see Khaskheli (21); micrographs not shown). The second approach of CSLM was to visualize the yoghurt area or phase of the mixture (yoghurt and Burghol) in more detail. During the &conditioning' period and especially after 6 days, the microstructure consisted of protein aggregates that had become more irregularly spaced and denser (micrograph not shown). This change in microstructure is probably a consequence of the swelling of the starch with exclusion of milk protein from the aqueous phase. In mixtures of milk and starch, the latter component preferably binds water, and this phenomenon has been reported in studies on the heat stability of milk (35). This denser microstructure was similar to strained yoghurt (Labneh; 220}260 g/kg total solids) reported by Kalab (36). Furthermore, at the end of the &conditioning' period greater aggregation of protein was also associated with the acid produced by microorganisms (7). When Burghol was mixed with whey obtained from yoghurt in order to visualize the hydrolysis of starch in acidic medium, no signi"cant di!erences were observed in the microstructure of starch granules when freshly mixed and at the end of the &conditioning' period (Fig. 8). Also, the addition of antimicrobial tablets to the mixture to control the microbial activity showed a relatively similar
pattern of the structure of the starch (21) (micrographs not shown). In contrast, the starch granules were clearly deformed to a lesser extent and were evenly distributed in the yoghurt/wheat #our mixture (Fig. 9). The majority of the particles were less swollen compared with the Burghol/ yoghurt mixture (micrograph not shown). Nevertheless, some of the starch granules appeared swollen, irregular in shape, and tended to aggregate (Fig. 9a*large arrow). However, the majority of starch granules were swollen to a limited extent, and a-amylase activity may have had an in#uence. The protein clusters originating from yoghurt were also evident, and evenly distributed. This is evidence with less swelling of the starch granules and the greater availability of water from solution of the milk protein (Fig. 9a*small arrow). At the end of the &conditioning' period, the starch granules were variable in shape and size. Some granules were small and spherical or large (lenticular) and/or oval; whilst others were swollen and irregular (Fig. 9b). When sodium azide was added to the mixture, the microstructure was similar to that shown in Fig. 9b, but the starch granules were more swollen, tended to stick together, and the protein matrix was more compact which might be due to the acidity which developed in the mixture during the &conditioning' period (7).
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Conclusion Substantial di!erences in the sensory character were noted between Kishk (set A) made with di!erent cereals (porridge oats, oat #our, wheat Burghol and wheat #our) and dairy base (unfermented milk, GDL and yoghurt). In particular the mouth-feel (&chalky', &mouth-coating&, &viscosity', &slimy', &sticky' characters) were associated with cereal type. Also, the type of acidulant (GDL vs. yoghurt) and unfermented milk a!ected the sensory pro"le of the product. An e!ect associated with process used to make Burghol was also identi"ed [i.e. Kishk (set B)]. The activity of a-amylase on macronutrients of the yoghurt/Burghol or wheat #our mixture of Kishk (set C) promoted a gradual linear decrease in the starch content of the mixture (Burghol or wheat #our based) up to the end of the &conditioning' period was evident, but no signi"cant di!erence between both mixtures was found. The addition of sodium azide in the mixture did not show considerable increase or decrease in the starch content of the appropriate mixtures. These observations were not in agreement to the level of a-amylase observed which was high in Burghol-based and low in wheat #our-based mixture. The extent of soluble nitrogen content in the di!erent Kishk doughs was associated primarily with the metabolic activity of microorganisms only in #our-based products, possibly due to the availability of protein for hydrolysis in wheat #our rather than the protective protein by starch in Burghol. The microstructure of yoghurt/Burghol or wheat #our mixture suggested that there was a physical change in starch granules rather than degradation. No di!erence was observed when sodium azide was mixed into the mixture. In addition, no signi"cant di!erences were also observed in the microstructure of the starch granules when whey from yoghurt was mixed with Burghol. The shrinkage of the protein phase in the mixture implied a loss of moisture in this region, and this in turn probably allowed hydration and consequent swelling of the starch grains. Acknowledgements The expert technical assistance of Mrs I. Hamilton, Miss A. Mair, Mrs C. Shankland and Mr T. McCreath is gratefully acknowledged. Mr E. A. Hunter and D. McNulty are thanked for helpful comments. Dr M. Khaskheli is indebted to the World Bank for "nancial support. This work was funded by the Scottish Executive Rural A!airs Department (SERAD). References 1 TAMIME, A. Y. AND O'CONNOR, T. P. Kishk*A dried fermented milk/cereal mixture. International Dairy Journal, 5, 109}128 (1995) 2 TAMIME, A. Y., MUIR, D. D., BARCLAY, M. N. I., KHASKHELI, M. AND MCNULTY, D. Laboratory-made Kishk from wheat, oat and barley: 1. Production and comparison of chemical and nutritional composition of Burghol. Food Research International, 30, 311}317 (1997)
3 MUIR, D. D., TAMIME, A. Y. AND HUNTER, E. A. Sensory properties of Kishk: comparison of products containing bovine and caprine milk. Journal of the Society of Dairy ¹echnology, 48, 123}127 (1995) 4 TAMIME, A. Y., MUIR, D. D., BARCLAY, M. N. I., KHASKHELI, M. AND MCNULTY, D. Laboratory-made Kishk from wheat, oat and barley: 2. Compositional quality and sensory properties. Food Research International, 30, 319}326 (1997) 5 TAMIME, A. Y., MUIR, D. D., KHASKHELI, M. AND BARCLAY, M. N. I. E!ect of processing conditions and raw materials on the properties of Kishk. 1. Compositional and microbiological qualities. ¸ebensmittel-=issenschaft und ¹echnologie, 33, 444}451 (2000) 6 YIU, S. H. Cereal Structure and relationship to nutritional quality. Food Microstructure, 8, 99}113 (1989) 7 IBANOGLU, S., IBANOGLU, E. AND AINSWORTH, P. E!ect of di!erent ingredients on the fermentation activity in trahana. Food Chemistry, 64, 103}106 (1999) 8 IBANOGLU, S., AINSWORTH, P. AND HAYES, G. D. Extrustion of trahana: e!ect of operating variables on starch gelatinization. Food Chemistry, 57, 541}544 (1996) 9 IBANOGLU, S. AND AINSWORTH, P. Kinetics of starch gelatinization during extrusion of trahana, a traditional Turkish wheat #our } yoghurt mixture. International Journal of Food Science and Nutrition, 48, 201}204 (1997) 10 HUNTER, E. A., MUIR, D. D. AND BRENNAN, R. M. Comparison of the performance of an external panel with an internal panel. In: Proceedings 4 e` mes Journees Europeennes Agro-Industry et Methods Statistique, 7}8 December. Dijon: pp. 77}85 (1995) 11 MUIR, D. D. AND HUNTER, E. A. Sensory evaluation of Cheddar cheese: order of tasting and carry over e!ects. Food Quality and Preference, 3, 141}145 (1991/2) 12 WILLIAMS, S. A. R., HUNTER, E. A., PARKER, T. G., SHANKLAND, C. E., BRENNAN, R. M. AND MUIR, D. D. DDASP: a statistical based system for design, data capture and analysis with the sensory pro"ling protocol. In: Proceedings 3e` me Congres Sensometrics, 19}21 June 1996, Nantes: pp. 48.1}48.3 (1996) 13 BRISDON, E. Y. ¹he Oxoid Manual, 6th Edn. Basingstoke: Unipath Ltd., pp. 38}39 (1990) 14 IDF. Determination of Non-Protein Nitrogen Content 2 Standard 20B. Brussels: International Dairy Federation (1993) 15 ANONYMOUS. Amylazyme a-Amylase Assay Procedure for the Measurement of Cereal and Microbial a-Amylase. Wicklow: Megazyme International (Ireland) Ltd., Ireland (1997) 16 ANONYMOUS. ¹otal Starch Procedure 2 Amyloglucosidase/ a-Amylase. Wicklow: Megazyme International (Ireland) Ltd., Ireland (1997) 17 LEWIS, D. F. Features of Food Microscope. Food Microstructure, 5, 1}18 (1986) 18 TAMIME, A. Y., KALAB, M. AND DAVIES, G. The e!ect of processing temperatures on microstructure and "rmness of Labneh made from cow's milk by the traditional method or by ultra"ltration. Food Structure, 10, 345}352 (1991) 19 KALAB, M. Practical aspects of electron microscopy in cheese research. In: MALIN, E. L. AND TUNICK, M. H. (Eds), Chemistry of Structure 2 Function Relationship in Cheese. New York: Plenum Press, pp. 247}276 (1995) 20 TAMIME, A. Y., BARCLAY, M. N. I., AMAROWICZ, A. M. AND MCNULTY, D. Kishk } a dried fermented milk/cereal mixture. 1. Composition of gross components, carbohydrates, organic acids and fatty acids. ¸ait, 79, 317}330 (1999) 21 KHASKHELI, M. Some Aspects of the Production and Quality Improvement of Fermented Milk/Cereal Mixture (Kishk), PhD thesis. Glasgow: University of Glasgow, U.K. (1998)
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22 OLASUPO, N. A., OLUKOYA, D. K. AND ODUNFA, S. A. Studies on local strains of amylolytic ¸actobacillus from Nigerian fermented foods. Nahrung, 40(1) 45}46 (1996) 23 GUY, E. J. AND JENNESS, R. Separation, concentration and properties of a-amylase from cow's milk Journal of Dairy Science, 41, 13}27 (1958) 24 LING, E. R. A ¹ext-book of Dairy Chemistry, Vol 1, 3rd Edn. London: Chapman & Hall, pp. 46}49 (1963) 25 WALSTRA, P. AND JENNESS, R. Dairy Chemistry and Physics. New York: John Wiley & Sons, pp. 137}138 and 411 (1984) 26 WHITNEY, R. McL. Proteins in milk. In: WONG, N. P., JENNESS, R., KEENEY, M. AND MARTH, E. H. (Eds.), Fundamentals of Dairy Chemistry, 3rd Edn. New York: Van Nostrand Reinhold, pp. 81}169 (1988) 27 TOWALSKI, Z. AND ROTHMAN, H. Enzymes and the Food and Beverages Industry. In: FRANSMAN, M., JUNNE, G. AND ROOBEEK, A. (Eds.) ¹he Biotechnology Revolution. Oxford: Blackwell Publishers, pp. 252}257 (1995) 28 BANKS, W., EVERS, A. D. AND MUIR, D. D. The location of alpha-amylase in developing cereal grains. Chemistry and Industry, 573}574 (1972)
29 KENT, N. L. AND EVERS, A. D. ¹echnology of Cereals, 4th Edn. Oxford: Elsevier Applied Science, pp. 66}68, 239}295 (1994) 30 ROBINSON, D. S. Food Biochemistry and Nutritional
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E!ect of Processing Conditions and Raw Materials on the Properties of Kishk 2. Sensory Pro"le and Microstructure D. D. Muir, A. Y. Tamime* and M. Khaskheli
D. D. Muir: Hannah Research Institute, Ayr KA6 5HL (Scotland) A. Y. Tamime, M. Khaskheli: SAC Auchincruive, Food Systems Division, Ayr KA6 5HW (Scotland) (Received March 14, 2000; accepted June 14, 2000)
Diwerences in sensory character of Kishk were associated with cereal type and dairy base. When oat products were used as the cereal component, the Kishks were similar, but products made from Burghol and wheat your diwered in mouth-feel. In addition, the Kishks made with Burghol or Burghol your were easily distinguished from products made from wheat your. The length of the *conditioning+ period only inyuenced the *acid+ character of Kishk made with a combination of Burghol and low-fat yoghurt. The starch content in the yoghurt/Burghol or wheat your mixture decreased linearly during the *conditioning+ period as a result of a-amylase activity. The microstructure of the Kishk doughs was consistent with the normal pattern of degradation of wheat starch in which much of the original granular structure is retained during the *conditioning+ period.
2000 Academic Press Keywords: Kishk; sensory attributes (aroma, #avour, aftertaste, mouth-feel); cereals; acidulants; &conditioning' period; microstructure
Introduction Most Kishk products are made from di!erent cereal products and fermented milk base by traditional methods of manufacture (1, 2). The sensory properties of Lebanese Kishk reconstituted with water and served as a hot porridge or gruel have been pro"led by Muir et al. (3). The product made with caprine milk was clearly distinguishable from the rest of the Kishk samples. Tamime et al. (4) found that the mouth-feel attributes (&grainy', &sticky' and &slimy' character) of Kishk were associated with the type of Burghol used (e.g. wheat, barley or oats). In contrast, much less is known of the e!ect of modifying the properties of the milk base (unfermented, chemically acidi"ed with D-glucono-d-lactone (GDL) and yoghurt), but the properties of these Kishks have been described elsewhere (5). In contrast to Burghol, #our is a fractionated whole grain. That is, the starchy endosperm is selectively separated from the bran and germ, then milled into smaller particles; thus increasing the accessibility to enzymolysis (6). During the &conditioning' period of Kishk-making (1), the cereal enzymes have the potential to degrade the * To whom correspondence should be addressed. Present address: 24 Queens Terrace, Ayr KA7 1DX (Scotland).
0023-6438/00/060452#10 $35.00/0 2000 Academic Press
carbohydrate and protein. In addition, further acid development by the starter culture could in#uence the quality of Kishk. No data has been reported on the role of the &conditioning' period in Kishk-making, but recently, some researchers (7, 8, 9) have studied the e!ect of di!erent ingredients (e.g. fresh onions, tomato puree, salt, baker's yeast and powder consisting of a mixture of paprika, dill and mint) on the &conditioning' period activity, and the kinetics of operating variables on starch gelatinization during extrusion of Trahan (Greek or Turkish Kishk) made with wheat #our and full-fat yoghurt. The objectives of this paper were: (a) to determine the e!ect of milk components in combination with a range of di!erent cereal types on the sensory properties of Kishks; (b) to study the e!ect of di!erent treatment of the cereals on the sensory character of Kishk; (c) to evaluate changes in the sensory pro"le of Kishk produced using di!erent &conditioning' periods; and (d) to investigate changes in the structure of cereal starch during the &conditioning' period.
Materials and Methods Manufacture of Kishk Three sets of Kishk samples (A, B and C) were produced by the same method described in an earlier study (5).
doi:10.1006/ fstl.2000.0687 All articles available online at http://www.idealibrary.com on
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Sensory proxling Sensory pro"ling was carried out using a protocol successfully applied to a diverse range of commercial samples (3). Initially, the panel of assessors and the sensory scientists agreed on lists of descriptors for the modalities: odour, #avour, aftertaste and mouth-feel. The panel were acclimatized to the sensory properties of Kishk using commercial samples. The attribute ratings were tested for ability to discriminate and redundant or poorly understood terms were deleted from, the additional descriptors inserted into, the experimental vocabulary. The "nal vocabulary, derived for commercial products, was applied without modi"cation to the laboratory-prepared Kishk in the present study. The pro"le comprised seven attributes to describe aroma (&overall intensity', &creamy/milky', &acid/vinegary/sharp', &fruity/sweet', &cooked', &cereal', &cardboard'), ten #avour attributes (&overall intensity', &creamy/milky', &acid/vinegary/sharp', &fruity/sweet', &cooked', &cereal', &cardboard', &apple', &bitter', &salty'), "ve descriptors of aftertaste (&overall intensity', &persistence', &acid/vinegary/sharp', &cereal', &cardboard'), and "ve terms used to describe mouth-feel (&viscosity', &grainy/#oury/chalky', &sticky/gluey', &slimy', &mouth-coating'). Assessors The panel of assessors was an external panel of 15 female nonsmokers, aged 39}55, whose sole duties were sensory characterization. The panel were selected on the basis of sensory acuity and consistency and are highly experienced in pro"ling a wide range of foods. Panel performance is assessed by the principles described by Hunter et al. (10). Sample preparation Kishk samples made from di!erent cereal types and dairy bases were treated in an identical fashion. Each dried powder was mixed with four parts cold tap water and brought to boiling point with continuous stirring. After simmering for 5 min with occasional stirring, the product was immediately served hot in ceramic cereal bowls. Sample presentation Sample assessment was carried out in isolated air-conditioned booths with controlled lighting. Assessors cleansed their palate with a plain, water biscuit and some cold water then rated each sample for the attributes listed above. Two samples were presented in each tasting session, and several sessions, i.e. four to six, were held on each day. The order of the presentation of samples was balanced (11). Rating of attributes was on an undi!erentiated scale with anchor points (absent, extremely strong) and was facilitated by an interactive, computer-assisted data collection system (12). Samples were pro"led twice. Data analysis Mean sample e!ects were computed by analysis of variance (ANOVA) and principal components analysis as
Table 1 Experimental treatments and levels Treatment Base type Cereal Inhibitor Test time Supplier
Levels Yoghurt; whey from yoghurt Burghol; wheat #our Sodium azide, antimicrobial tablets Fresh; 2, 4 and 6 days Two di!erent sources
detailed by Muir et al. (3). To further simplify interpretation of the sensory space maps, Factor Rotation (varimax) was applied to the Principal Component Analysis (PCA).
*Conditioning+ period To assess the role of the enzymatic hydrolysis (microbial and a-amylase activity) of the macronutrients of the dough during the &conditioning' period, an experiment was conducted to observe the possible enzymatic e!ects as well as the structural changes. The experimental treatments and levels constituted a randomized complete block design replicated one time with repeated measurements at four time-points. The treatment had a factorial structure shown in Table 1. Sodium azide (Fisher Scienti"c Ltd., U.K.) was added at a rate of 0.2 g/kg to inhibit the growth of microorganisms including the starter culture (13). The bacterial activity was monitored by measuring the soluble nitrogen content in the dough which is similar, in principle, to the maturity index in cheese; however, sodium azide is a hazardous chemical leading to explosion at high temperatures which makes the test for soluble nitrogen very dangerous. Parallel samples were used where the sodium azide was replaced with antimicrobial tablets (50 tablets/kg dough; Broad Spectrum Microtab] II, D and F Control Systems Inc., U.S.A.). The soluble nitrogen content, a-amylase activity and starch content were determined according to the method described by IDF (14) and Anonymous (15, 16), respectively.
Microscopic analysis A Laser Scanning Confocal Microscope (LSCM) MRC1000 (Bio-Rad Microxience Ltd., U.K.) was used to study the microstructure of the dough during the &conditioning' period. The samples were "xed in a 25 g/kg aqueous glutaraldehyde solution (TAAB Laboratories Equipment Ltd., U.K.) as described by Lewis (17), Tamime et al. (18) and Kalab (19), washed with distilled water, dehydrated in graded ethanol (700, 800, 900, 1000 g/kg) and embedded in LR white acrylic resin (London Resin Company Ltd., U.K.). The embedded samples were sectioned using an UB Ultratone (type 8801A; LKB-Producter A/B, Sweden) and stained with Acridine Orange (1 g/kg; Sigma Company Ltd., U.K.). The images were recorded and stored on the hard disc of the computing system connected to the microscope.
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Table 2 E!ect of di!erent cereal type and dairy base on the sensory ratings of Kishk (set A) Treatment e!ect (0}100) Porridge oats Attribute Odour Intensity Creamy Acid Fruity/sweet Cooked Cereal Cardboard Flavour Intensity Creamy Acid Fruity/sweet Cooked Cereal Cardboard Apple Bitter Salty Aftertaste Intensity Acid Cereal Cardboard Mouth-feel Viscosity Chalky Sticky Slimy Mouth-coating
Oat #our
Burghol
Wheat #our
M?
GDL@
YA
M
GDL
Y
M
GDL
Y
M
GDL
Y
SEDB
47.5 30.6 5.7 28.1 42.4 36.3 18.4
48.8 14.3 29.8 16.2 42.1 34.8 14.0
43.4 19.2 22.6 18.6 38.4 33.0 10.0
50.3 34.2 2.7 30.5 43.5 40.9 17.4
44.5 12.0 27.7 13.0 37.7 32.9 15.7
37.6 12.9 19.8 16.9 32.1 25.8 9.3
47.7 25.5 9.8 29.2 38.0 38.0 10.5
46.5 14.1 26.5 17.8 40.7 35.9 11.7
41.8 17.3 18.9 18.4 34.0 34.9 11.5
47.0 26.0 10.1 25.1 40.8 33.6 12.6
47.2 11.5 33.0 16.5 39.3 26.0 10.5
46.1 11.5 31.0 14.7 34.0 17.8 15.3
3.92 3.35 4.83 3.49 3.92 3.63 3.28
48.5 31.4 10.8 27.1 46.4 42.0 28.3 4.3 3.0 7.1
53.9 21.0 40.4 16.9 44.5 37.6 16.2 10.1 9.9 16.8
57.6 19.3 48.3 20.1 43.2 35.4 18.8 8.0 11.3 17.5
43.1 30.6 4.8 25.4 46.1 38.5 27.6 0.5 1.4 1.8
52.8 18.0 43.2 18.1 40.7 36.3 21.0 8.1 6.9 18.4
58.1 21.5 56.2 25.2 38.8 34.4 20.0 11.6 9.5 21.5
48.9 28.0 14.5 28.0 39.2 48.6 19.7 2.3 2.6 6.6
53.3 24.3 32.9 28.1 40.8 45.8 11.0 6.6 5.1 19.2
57.7 18.8 44.9 26.2 35.5 41.9 14.2 13.8 9.1 20.9
48.1 30.7 10.1 35.5 44.9 33.8 21.4 3.4 4.8 6.7
50.7 18.5 52.3 23.9 42.2 29.1 23.0 7.3 11.8 19.9
61.0 17.2 60.2 21.4 37.4 26.6 22.0 6.9 16.8 23.5
4.34 3.31 5.88 3.56 3.69 3.50 3.67 2.41 2.33 3.31
40.8 8.3 35.0 23.4
42.0 30.4 33.0 12.5
43.5 36.7 30.1 12.2
38.0 2.8 35.4 21.7
43.4 33.7 31.3 20.5
48.0 43.5 27.4 15.8
42.9 8.7 37.1 12.3
42.0 24.9 37.3 9.7
45.8 40.6 31.7 13.0
39.5 7.3 29.2 22.2
51.6 44.9 25.3 15.7
58.4 51.6 21.1 16.9
2.66 4.36 3.21 3.50
69.4 33.3 56.6 23.0 45.8
71.3 29.0 64.0 30.1 48.7
66.5 31.6 65.4 29.8 49.8
67.5 39.7 52.8 16.4 47.8
65.5 27.6 58.3 29.4 47.9
63.1 24.4 57.4 29.0 47.1
67.9 56.0 20.7 2.7 40.6
64.4 56.7 22.4 3.5 37.9
65.7 54.9 25.7 4.2 42.2
65.4 21.8 67.2 52.3 46.6
66.8 17.3 74.1 64.2 49.9
66.5 20.0 76.2 70.3 54.5
4.86 4.04 3.34 4.71 3.66
? Unfermented milk. @ D-Glucono-d-lactone. A Yoghurt. B Standard error of di!erence of mean.
Results and Discussion Gross chemical composition of Kishk The average chemical composition of Kishk samples (sets A, B and C) were reported by Tamime et al. (5). The di!erences between samples were mainly associated with cereal type and processing conditions; however, the chemical composition of the experimental Kishks were within the range of commercial Kishk samples sold in the Lebanese market (20). Sensory properties~The ewect of dairy base and cereal type Kishks (set A) The di!erences in the sensory quality of the Kishk was mainly associated with the type of dairy base used (Table 2). For example, the product made with unfermented milk was much more &creamy', &fruity/sweet', &intensity' (odour and #avour), &cereal', &cardboard' (odour #avour and aftertaste), less &acid' (odour, #avour and aftertaste), and &salty', &apple', &bitter' (#avour) to the corresponding products made with yoghurt. The GDLbased Kishk had slightly higher scores for &cereal' (odour,
#avour and aftertaste), &cooked' (odour and #avour) and &acid' (odour), but less for &creamy' (odour), &acid' (#avour and aftertaste), and &bitter', &salty' (#avour) when compared with Kishk made with yoghurt. Thus, the type of acidulant (i.e. GDL vs. yoghurt) also a!ected the sensory pro"le of the product. The mouth-feel attribute of Kishk made with unfermented milk was perceived as slightly more &viscous' and &chalky', but less &sticky', &slimy' and &mouth-coating'. Although the Kishk made with GDL or yoghurt had similar mouth-feel ratings, the latter product was perceived to be more &sticky', &mouth-coating' and &slimy'; these characters were in#uenced by the cereal type used. There was no evidence of systematic di!erences in odour, #avour, (except &fruity/sweet') or aftertaste (except &intensity') being associated with cereal type. While appreciable di!erences were found between mouth-feel characters (&chalky', &sticky', &slimy') these attributes were associated with the cereal type. Principal component analyses (PCA) (with Factor Rotation : varimax) were used to simplify interpretation of the main di!erences between products. Factor 1 explained 31% of variance and Factor 2 a further 25%. For
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Fig. 1 Sensory space maps based on Factor scores after PCA for Kishk (set A) made with di!erent cereals and milk bases. 䊏 䊐 Unfermented Milk; 䊉 䊊 GDL; 䉱 䉭 yoghurt. Closed symbols represent rolled oats or Burghol. Open symbols represent oat or wheat #our
Fig. 2 Star plots for the e!ect of cereal type on perceived mouth-feel attribute of Kishk (set A). A and B are di!erent sources of oats and wheat products
convenience, the mean scores for each of the 12 combinations of cereal and dairy base were used to construct separate sensory space maps for oat- and wheat-based products. Factor 1 was associated with cereal type, and Factor 2 with dairy base. For oat-based products, there was a clear progression on Factor 2 from unfermented milk through GDL-acidi"ed milk to yoghurt-based product (Fig. 1*oat). There is no evidence of a signi"cant di!erence between Kishk made from rolled oats or oat #our (Factor 1). The separation of Kishk on Factor 2 was associated with di!erences in #avour intensity * in particular, &acidic', &bitter', and &salty' character (data not shown). In wheat-based Kishk, a di!erent picture emerged (Fig. 1*wheat). Here, the products were clearly separated in terms of particle size by the scores on Factor 1. The
Kishk made from wheat #our was distinguished by its &sticky' and &slimy' character (ratings were 67}76 and 52}70, respectively), and that from Burghol by its &chalky' nature (55}57; see Table 2). On the other hand, separation on Factor 2 was essentially the same as that observed for all oat products, i.e. there was a progression from unfermented milk to yoghurt in terms of #avour &intensity'. To aid comparison of the e!ect of the cereal type on the perceived mouth-feel character of Kishk, a star plot was constructed (Fig. 2). Each attribute is assigned a vector, the length of which is determined by the magnitude of the attribute, expressed as a proportion of the maximum value within the sample set. The major variations in attributes were in &chalky', &slimy' and &sticky' characters. Variation between the plots for the Kishks based on oat
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Fig. 3 Sensory space maps based on Factor scores after PCA of Kishk (set B) made with di!erent wheat products. Unfermented milk GDL Yoghurt Burghol 䊏 䊉 䉱 Burghol #our 䊏 䊉 䉱 Wheat #our 䊐 䊊 䉭 (a) and corresponding vector loading for Factors 1 and 2. 䊏 Mouth-feel, 䉱 aftertaste, 䊉 #avour (b)
were minor. In contrast, the plots for Burghol and wheat #our demonstrated a clear di!erence. Burghol-based Kishk contrasted quite di!erently to those made from wheat #our indicating the in#uence of the particle size of cereals and method of preparation, i.e. parboiled cracked wheat vs. wheat #our. There were clear indications from Figs. 1 and 2 that the e!ect of cereal particle size (irrespective of the dairy base) was important. The e!ect of treatment (i.e. cereal type, dairy base and particle size) on the sensory attributes was examined by ANOVA, and the signi"cant treatment effects (data not shown) could be summarized as follows: (a) cereal type had only e!ect on &fruit/sweet' (#avour) (P(0.01), and &intensity' (aftertaste), &chalky', &sticky' and &slimy' (mouth-feel) (P(0.001); (b) the dairy base had the greatest e!ect on sensory characters (P(0.001) with the exception of &cardboard' (odour), &cooked' and &cardboard' (#avour), and &viscosity', &chalky' and &mouthcoating' (mouth-feel); and (c) the di!erences between the cereals supplied by di!erent sources was limited to changes in &intensity', &cooked' (odour) and &slimy' (mouth-feel) (P(0.001); &cooked', &cardboard' (#avour) and &chalky' (mouth-feel) (P(0.01), and &acid' (odour) (P(0.05). The e!ect of cereal particle size was particularly important for mouth-feel characters [&chalky', &sticky', &slimy' (P(0.001)], &mouth-coating' (P(0.01), and aftertaste [&cereal' (P(0.001), &intensity', &acid' and &cardboard' (P(0.01)]. The interaction of the cereal type;dairy base was only signi"cant (P(0.05) for &cardboard' (odour) and &fruity/sweet' (#avour), whilst the dairy base;cereal particle size interaction was only signi"cant for #avour attributes &apple' (P(0.01) and &fruity/sweet' (P(0.05). The cereal type;particle size interaction was highly signi"cant for mouth-feel (&chalky', &sticky', &slimy' and &mouth-coating'; P(0.001), and for #avour (&cereal',
&apple' and &bitter'; P(0.001); on odour and aftertaste (&cereal'; P(0.01 and &acid', P(0.05) and for aftertaste (&intensity'; P(0.05). The dairy base;size of the cereal interaction was only signi"cant on &intensity' (aftertaste; P(0.001), &cereal' (odour; P(0.01) and &acid' (#avour and aftertaste; P(0.01).
Sensory properties~The ewect of particle size of wheat-based Kishks (set B) The sensory rating for the Kishks made with Burghol or Burghol #our were very similar, but di!erent from samples made with wheat #our; the results are wholly consistent with those reported for Kishk samples (set A) (data not shown; see Table 2). Once again PCA (with Factor Rotation) was used to simplify interpretation of di!erent products. Two Factors explained 35.3 and 30.8% of variance, respectively. In this instance, the Kishk samples were separated in the "rst Factor in terms of dairy base (Fig. 3a) while Factor 2 was associated with di!erences in particle size. As had been observed previously with sample set A, the progression from unfermented milk to yoghurt was associated with an increase in #avour &intensity', particularly with &acidic', &bitter', &salty', and &cereal' notes (Fig. 3b). In addition, separation on Factor 2 was associated with &chalky' mouth-feel for Burghol with a transition to &sticky' and &slimy' character for wheat #our. Burghol #our was only slightly separated from Burghol. The di!erences in sensory character were not simply related to particle size because wheat #our was di!erent from Burghol #our. On the other hand, the di!erences between Burghol and Burghol #our were modest. These results suggest that the di!erences between products are associated with the production method used to produce Burghol, not with particle size per se (1).
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Table 3 Signi"cant changes in ratings of sensory attributes (0}100) during the &conditioning' period of the Kishk dough (set C) Length of the secondary fermentation (days) Attribute Odour Intensity Creamy Acid Fruity/sweet Flavour Intensity Creamy Apple Acid Salty Aftertaste Intensity Acid Persistence
0
2
4
6
SED?
36.2 13.0 5.1 18.5
36.3 14.6 4.7 15.9
36.6 7.7 13.8 13.2
41.9 8.8 19.6 14.4
2.01 2.14 2.44 1.52
50.6 19.1 2.5 27.3 21.9
53.7 19.8 7.9 43.4 30.0
59.9 18.3 8.6 53.7 34.4
64.5 9.8 9.1 60.3 36.8
1.69 4.43 1.60 5.00 3.03
41.4 14.2 38.6
45.7 36.3 45.5
50.7 42.6 48.0
53.7 47.1 52.8
2.25 2.82 2.44
Fig. 4 a-amylase activity (units/g) of wheat cereals/yoghurt mixture (set C) during the &conditioning' period. 䊉 Burghol# yoghurt; 䊊 Burghol#yoghurt#sodium azide; 䉱 Wheat #our#yoghurt; 䉭 Wheat #our#yoghurt#sodium azide
? Standard error of di!erence of mean.
Sensory character~The ewect of *conditioning+ period on Kishk (set C) The changes in sensory pro"les as a function of the length of the &conditioning' period were investigated by pro"ling the Kishk dough when fresh (0 days), and at 2, 4 and 6 days (control). No signi"cant treatment e!ects were observed for &cooked', &cereal' or &cardboard' odour; for &fruity', &cooked', &cereal', &cardboard' or &bitter' #avour; or for &viscous', &grainy', &slimy', &sticky' or &mouth-coating' aspects of mouth-feel. However, there were signi"cant e!ects associated with the attributes shown in Table 3. The pattern of change di!ered between attributes. The most marked changes were associated with &acid' character for odour, #avour and aftertaste. There tended to be a greater change in the end of the &conditioning' period than at the start. Odour and #avour &intensity' and the &intensity' of aftertaste and its persistence followed a similar pattern (Table 3). On the other hand, &creamy' odour and #avour, and &fruity' odour declined during the &conditioning' period. &Apple' #avour receded, albeit from a low base, over the period studied. Although there was no evidence from chemical analysis of changes in salt content the perception of saltiness increased during the &conditioning' period. The main changes were in &acid' character, and these corresponded to growth of the yoghurt micro#ora during the &conditioning' period (5).
Amylase activity (set C) The a-amylase activity during the &conditioning' period is shown in Fig. 4. This enzyme activity (units/g) was detected in yoghurt, Burghol and wheat #our at 0.019, 0.012 and 0.046}0.069, respectively (21; data not shown). The presence of this enzyme in ¸actobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus has never been reported previously, but has recently been
noted in many strains of lactobacilli isolated from Nigerian fermented foods (22). However, protein fractions precipitated from whey, concentrated milk or serum contained a-amylase activity (23}27), therefore, such as enzyme could then be present in yoghurt. A range of a-amylase activity in wheat #our supplied from di!erent sources was evident (21), and this could be due to factors such as growing, harvesting or milling (28). The a-amylase activity increased slightly in wheat #our-based yoghurt mixtures on the second day of the &conditioning' period and then decreased (Fig. 4). In contrast, in Burghol-based mixtures the a-amylase activity increased progressively and sharply after 4 days until the end of the &conditioning' period. This is probably due to the destruction of a-amylase activity between the pericaptesta and endosperm-germ fractions (29). During the re"ning of #our, a-amylase activity is lost. However, in the presence of moisture originating from yoghurt, the cereal tends to swell or becomes soft encouraging the release of a-amylase into the yoghurt/Burghol mixture (30). The changes in a-amylase activity in the wheat #our/ yoghurt mixture were comparatively small and unlikely to be of practical signi"cance (28, 30}32), and the presence of sodium azide did not cause any inhibition to a-amylase (see Fig. 4). The signi"cance of treatment e!ects were cereal type (P(0.01), &conditioning' period (CP) and cereal type;CP (P(0.001), and yoghurt;CP (P(0.05).
Starch (set C) The starch content in all the cereal/yoghurt mixtures including the samples containing sodium azide were reduced by ca. 40% at the end of the secondary fermentation state (Fig. 5). The reduction in the starch content in all the samples was similar and relatively linear. Analysis of variance showed that signi"cant di!erences for CP (P(0.001), cereal type;CP (P(0.01) and yoghurt;CP (P(0.05).
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Fig. 7 Microstructure of starchy endosperm of yoghurt/Burghol mixture (set C) during the &conditioning' period when fresh; arrow illustrate starch granules
Fig. 5 Decrease in starch content (expressed as %) of yoghurt/wheat cereals mixtures (set C) during the &conditioning' period. 䊉 Burghol#yoghurt; 䊊 Burghol#yoghurt# sodium azide; 䉱 Wheat #our#yoghurt; 䉭 Wheat #our# yoghurt#sodium azide
Fig. 6 Soluble nitrogen content (g/kg) of wheat cereal/yoghurt mixtures (set C) during the &conditioning' period. 䊉 Burghol#yoghurt; 䊊 Burghol#yoghurt#sodium azide; 䉱 Wheat #our#yoghurt; 䉭 Wheat #our#yoghurt#sodium azide
Soluble nitrogen (set C) The pro"le of increase of soluble nitrogen content in the cereal type/yoghurt mixtures during the &conditioning' period is shown in Fig. 6. This re#ects primarily the metabolic activity of microorganisms of the protein which is similar to the maturity index of cheese during the storage period (5, 26). No signi"cant increase in the soluble nitrogen content was evident in Burghol-based mixtures, whilst in #our-based products a sharp increase was obtained. This could be attributed to the availability of protein for hydrolysis in wheat #our as compared to the more protective starch cellular structure of Burghol. Also, the particle size of the cereal may have played
a contributory role a!ecting the rate of protein hydrolysis. The addition of antimicrobial tablets to the mixture, in part, controlled the microbial activity, and a lower amount of soluble nitrogen was produced (see Fig. 6). Furthermore, the yoghurt micro#ora, yeasts or moulds were not recovered from any of the dough mixtures (up to 6 days) within the sensitivity of the test (i.e. 10\ dilution) for all the samples containing sodium azide which has a bactericidal e!ect against Gram-positive bacteria; however, sodium azide controlled, in part, certain species of nonactic acid bacteria (13, 21). Analysis of variance of treatment e!ects were signi"cant (P(0.01) for cereal type, CP, cereal type;CP and cereal type;CP yoghurt.
Microstructure of the Kishk dough (set C) Confocal scanning laser microscopy (CSLM) revealed information on the "ne structure of Kishk and its constituents, but the relatively large particle size and uneven distribution of the constituents makes obtaining a single overall view of the structure di$cult (33). However, selected structural entities can be identi"ed at all stages of the &conditioning' period and the changes during processing can be deduced. The structural entities selected were the cereal endosperm tissue, the &free' yoghurt regions, and the interphase between the two. The starchy endosperm of yoghurt/Burghol mixture when fresh are shown in Fig. 7. The starch consisted of a population of granules which were essentially oval in shape. Some granules retained the lenticular forms of type A wheat starch, but others were swollen and deformed. The deformation was possibly in#uenced by the manufacturing stages of Burghol where the grains were steeped in boiling water, dried to its original moisture content, rehydrated with ca. 200 g/kg moisture, cracked and dried (1). Similar microstructural changes in wheat starch dispersions during heating and cooling have been reported by Langton and Hermansson (34). The microstructure of starch granules at the end of the &conditioning' period were more irregular in shape, swollen and tended to stick together; even when sodium azide was added to the mixture to control the microbial
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Fig. 8 Starchy endosperm structure of whey/Burghol mixture when fresh (a) and after six days (b) during the &conditioning' period; arrows illustrate starch granules
Fig. 9 Microstructure of starch granules in yoghurt/wheat #our mixture (set C) during the &conditioning' period [fresh (a) and after six days (b)]; arrows show starch granules and white specks illustrate protein aggregates
activity, no di!erence(s) was observed in the behaviour of the starch granules (see Khaskheli (21); micrographs not shown). The second approach of CSLM was to visualize the yoghurt area or phase of the mixture (yoghurt and Burghol) in more detail. During the &conditioning' period and especially after 6 days, the microstructure consisted of protein aggregates that had become more irregularly spaced and denser (micrograph not shown). This change in microstructure is probably a consequence of the swelling of the starch with exclusion of milk protein from the aqueous phase. In mixtures of milk and starch, the latter component preferably binds water, and this phenomenon has been reported in studies on the heat stability of milk (35). This denser microstructure was similar to strained yoghurt (Labneh; 220}260 g/kg total solids) reported by Kalab (36). Furthermore, at the end of the &conditioning' period greater aggregation of protein was also associated with the acid produced by microorganisms (7). When Burghol was mixed with whey obtained from yoghurt in order to visualize the hydrolysis of starch in acidic medium, no signi"cant di!erences were observed in the microstructure of starch granules when freshly mixed and at the end of the &conditioning' period (Fig. 8). Also, the addition of antimicrobial tablets to the mixture to control the microbial activity showed a relatively similar
pattern of the structure of the starch (21) (micrographs not shown). In contrast, the starch granules were clearly deformed to a lesser extent and were evenly distributed in the yoghurt/wheat #our mixture (Fig. 9). The majority of the particles were less swollen compared with the Burghol/ yoghurt mixture (micrograph not shown). Nevertheless, some of the starch granules appeared swollen, irregular in shape, and tended to aggregate (Fig. 9a*large arrow). However, the majority of starch granules were swollen to a limited extent, and a-amylase activity may have had an in#uence. The protein clusters originating from yoghurt were also evident, and evenly distributed. This is evidence with less swelling of the starch granules and the greater availability of water from solution of the milk protein (Fig. 9a*small arrow). At the end of the &conditioning' period, the starch granules were variable in shape and size. Some granules were small and spherical or large (lenticular) and/or oval; whilst others were swollen and irregular (Fig. 9b). When sodium azide was added to the mixture, the microstructure was similar to that shown in Fig. 9b, but the starch granules were more swollen, tended to stick together, and the protein matrix was more compact which might be due to the acidity which developed in the mixture during the &conditioning' period (7).
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Conclusion Substantial di!erences in the sensory character were noted between Kishk (set A) made with di!erent cereals (porridge oats, oat #our, wheat Burghol and wheat #our) and dairy base (unfermented milk, GDL and yoghurt). In particular the mouth-feel (&chalky', &mouth-coating&, &viscosity', &slimy', &sticky' characters) were associated with cereal type. Also, the type of acidulant (GDL vs. yoghurt) and unfermented milk a!ected the sensory pro"le of the product. An e!ect associated with process used to make Burghol was also identi"ed [i.e. Kishk (set B)]. The activity of a-amylase on macronutrients of the yoghurt/Burghol or wheat #our mixture of Kishk (set C) promoted a gradual linear decrease in the starch content of the mixture (Burghol or wheat #our based) up to the end of the &conditioning' period was evident, but no signi"cant di!erence between both mixtures was found. The addition of sodium azide in the mixture did not show considerable increase or decrease in the starch content of the appropriate mixtures. These observations were not in agreement to the level of a-amylase observed which was high in Burghol-based and low in wheat #our-based mixture. The extent of soluble nitrogen content in the di!erent Kishk doughs was associated primarily with the metabolic activity of microorganisms only in #our-based products, possibly due to the availability of protein for hydrolysis in wheat #our rather than the protective protein by starch in Burghol. The microstructure of yoghurt/Burghol or wheat #our mixture suggested that there was a physical change in starch granules rather than degradation. No di!erence was observed when sodium azide was mixed into the mixture. In addition, no signi"cant di!erences were also observed in the microstructure of the starch granules when whey from yoghurt was mixed with Burghol. The shrinkage of the protein phase in the mixture implied a loss of moisture in this region, and this in turn probably allowed hydration and consequent swelling of the starch grains. Acknowledgements The expert technical assistance of Mrs I. Hamilton, Miss A. Mair, Mrs C. Shankland and Mr T. McCreath is gratefully acknowledged. Mr E. A. Hunter and D. McNulty are thanked for helpful comments. Dr M. Khaskheli is indebted to the World Bank for "nancial support. This work was funded by the Scottish Executive Rural A!airs Department (SERAD). References 1 TAMIME, A. Y. AND O'CONNOR, T. P. Kishk*A dried fermented milk/cereal mixture. International Dairy Journal, 5, 109}128 (1995) 2 TAMIME, A. Y., MUIR, D. D., BARCLAY, M. N. I., KHASKHELI, M. AND MCNULTY, D. Laboratory-made Kishk from wheat, oat and barley: 1. Production and comparison of chemical and nutritional composition of Burghol. Food Research International, 30, 311}317 (1997)
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