A survey of the dielectric properties of meats and ingredients used in meat product manufacture

MEAT SCIENCE Meat Science 69 (2005) 589–602 www.elsevier.com/locate/meatsci

A survey of the dielectric properties of meats and ingredients used in meat product manufacture J.G. Lyng *, L. Zhang, N.P. Brunton Department of Food Science, Faculty of Agriculture, University College, Dublin, Belfield, Dublin 4, Ireland Received 24 July 2004; accepted 2 September 2004

Abstract The objective of the present study was to improve understanding of interactions between microwave (MW) and radio frequency (RF) radiation and meat/meat products. Dielectric properties at 27.12, 915 and 2450 MHz of lean, fat, aqueous solutions/suspensions and meat blends of typical ingredients used in meat product manufacture were measured. In addition temperature rises of ingredient/meat blends were compared following RF or MW heating. Frequency affected dielectric properties as did composition, with fat having lower dielectric activity than lean. Dielectric properties at MW frequencies appeared more sensitive to composition changes. Ingredients could be subdivided into groups having either lower or higher dielectric activity than lean, with concentration influencing which group an ingredient fell into. When low and high dielectric activity ingredients were incorporated into lean meats dielectric properties did not correlate well with temperature rises indicating the importance of other factors in addition to dielectric properties in determining temperature rise.
2004 Elsevier Ltd. All rights reserved. Keywords: Dielectric properties; Microwave; Radio frequency; Meat; Ingredients

1. Introduction Microwave (MW) and radio frequency (RF) heating of foodstuffs have been recognized since the early 1940s (Decareau, 1985). Commercial food processing applications of MW include cooking, thawing, tempering, drying, freeze-drying, pasteurisation, sterilization, baking heating and re-heating (Ayappa, Davis, Davis, & Gordon, 1991) while RF energy has been used for baking of snack foods (Rice, 1993), and pasteurising and sterilising meat products (Bengtsson & Green, 1970; Houben, van Roon, & Krol, 1990; Laycock, Piyasena, & Mittal, 2003; van Roon, Houben, Koolmees, & Vliet, 1994). The dielectric properties of foods

*

Corresponding author. Tel.: +353 1 716 7710; fax: +353 1 716 1147. E-mail address: [email protected] (J.G. Lyng). 0309-1740/$ - see front matter
2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.meatsci.2004.09.011

are important in understanding and modelling food behaviour in RF and MW fields. These properties of materials determine the interaction between the foodstuff and electromagnetic energy and are key factors in determining the efficiency of RF and MW heating. The dielectric properties of materials that are of interest in most applications can be defined in terms of their relative permittivity (e) (i.e. e = e 0
je00 ), where the real part, e 0 is the dielectric constant, the imaginary part, e00 , is the dielectric loss factor. e 0 is associated with the potential for electrical energy storage in the material while e00 is related to the electrical energy dissipation in the material. Cooking and heating of meat and meat products is an area where MW and RF radiation has found applications at domestic level but which also has potential at industrial level. While a reasonable amount of information has been published on the dielectric properties of meat and meat products

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Table 1 A selection of published dielectric property data for fish/meat and fish/meat products Freq (MHz)

Product

e 0 (Freq (MHz))

e00 (Freq (MHz))

Bengtsson, Melin, Remi, and So¨derlind (1963)

10–200

Van Dyke, Wang, and Goldblith (1969) Kent (1970) Bengtsson and Risman (1971) Kent (1972) Ohlsson, Henriques, and Bengtsson (1974) To, Mudgett, Wang, Goldblith, and Decareau (1974)

915 10,000 2800 10,000 900 and 2800 300, 915 and 2450

Kent (1975) Lee, Kim, and Lee (1983)

915 0.1, 0.75, 7.5 and 15

Tran and Stuchly (1987)

100–2500

Tanaka, Mallikarjunan, and Hung (1999) Tanaka, Mallikarjunan, Kim, and Hung (2000) Kent, Kno¨chel, Daschner, and Berger (2001) Lyng, Scully, McKenna, Hunter, and Molloy (2002) Sipahioglu, Barringer, Taub, and Yang (2003a) Sipahioglu, Barringer, Taub, and Prakash (2003b) Zhang, Lyng, Brunton, Morgan, and McKenna (2004)

300–3000 300–3000 200–12,000 2430 2450 915 and 2450 27.12, 915 and 2450

Beef lean at 10 C Codfish at 10 C Reconst. ground beef (25 C) Fish meal Beef Fish meal Meat emulsion Raw beef Cooked beef Raw turkey Cooked turkey Fish (Frozen) Sardine starch (20%) paste Sardine starch (50%) paste Beef (Temperature vs.) Beef liver (Temperature vs.) Chicken (Temperature vs.) Salmon (Temperature vs.) Shrimp Marinated chicken breast (3–75 C) Chicken Beefburgers (Composition vs.) Ham Turkey Comminuted meats (5-85 C)

70 (100)–67 (200) 72.8 (100)–68.9 (200) NA 2.2 (10,000) 47.7 (2800) 2.06–3.02 (10,000) 56.9 (900)–57.9 (2800) 55 (2450)–58 (915) 29(2450)–34 (915)–39 (300) 52 (2450)–60 (915)–67 (300) 37 (2450)–41 (915)–47 (300) 3.59–3.7 (915) 2.97 3.54 48.9 (2400)–75.4 (100) 46.6 (2400)–70.3 (100) 52.3 (2400)–74.2 (100) 49.8 (2400)–66.5 (100) 50 (3000)–70 (300) 45 (3000)–70 (300) 37 (12,000)–70 (200) 37.9–40 (2430) 12–50 (2450) 44 (2450)–56 (915) 29.97 (2450)–47.85 (27)

91 (100)–87.1 (200) 123.6 (100)–60.63 (200) 18 (915) 0.5 (10,000) 13.4 (2800) 0.018–0.452 (10,000) 18.3 (900)–17.3 (2800) 25 (2450)–27 (915)–70 (300) 10–55 25(2450)–30 (915)–160 (300) 20 (2450)–27(915)–75 (300) 0.214–0.34 (915) 0.36 0.44 18 (2400)–194.3 (100) 22.9 (2400)–166.4 (100) 17.7 (2400)–147 (100) 17.2 (2400)–144.7 (100) 20 (3000)–60 (300) 8 (3000)–98 (300) 5 (12,000)–90 (200) 11.8–17.8 (2430) 13–130 (2450) 20 (2450)–180 (915) 16.24 (2450)–1631.39 (27)

J.G. Lyng et al. / Meat Science 69 (2005) 589–602

Author

J.G. Lyng et al. / Meat Science 69 (2005) 589–602

(Table 1), different methods have been used to produce the data which has also been recorded at different frequencies and temperatures making it difficult to cross compare results. Although lean and fat meats are principle ingredients in processed meat products other non-meat ingredients are usually incorporated which have various functions. Examples of non-meat ingredients include salt (flavour, water binding, and preservation) and seasoning (flavour), nitrates and nitrites (colour and antimicrobial), proteins (increase nutritional value and aid in gelation), bulking agents such as starch and artificial colourings. Table 2 lists a selection of publications which give information on dielectric properties of some of these ingredients and serves to illustrate once again the difficulty in comparing this data due to differences in the measurement conditions. Overall the meat and ingredients used in meat product manufacture are likely to vary in their dielectric properties and their addition to products can potentially influence interaction between RF or MW radiation. Therefore, for a complete understanding of the interaction between meat products and dielectric fields a good knowledge of the relative dielectric properties of a broad range of meat and dry ingredients is required. For RF and MW cooking of meats, frequencies are restricted to the Industrial Scientific and Medical (ISM) frequencies (Brennan, Butters, Cowell, & Lilly, 1976). The objectives of the current study were to improve understanding of MW and RF interaction with meats by comparing the dielectric properties of lean and fat meat at extremes of RF and MW ISM frequencies while also ranking the dielectric properties of solutions/suspensions of selected meat product ingredients when prepared at a standard concentration of 5%. A further objective was to evaluate the dielectric properties of solutions/suspensions of selected meat product ingredients at typical usage levels and finally to evaluate the influence of blending selected meat ingredients into lean meat at normal usage levels.

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2. Materials and methods 2.1. Lean meat and pork fat preparation Five fresh lean meats (chicken (breast), lamb (leg), beef (forequarter trimmings), pork (shoulder) and turkey (breast) and one source of meat fat (pork back fat) were sourced from a local butcher (Hickeys, Bird Avenue, Dublin, Ireland). Excess fat was trimmed from both lean beef and lamb and the bone was removed from the latter while traces of lean were removed from the pork back fat. Lean meat was ground through a plate with 3.5 mm diameter holes while fat was ground through a 10 mm plate using a mechanical mincer (Model No. TS8E, Tritacarne, Omas, Italy). Each of the meats was blended with a household blender (Model No. 4259, Braun, Verbraucherrefera, 61466 Kronberg, Germany) with double blade slicer for 60 s at knife speed one and 90 s at knife speed two. The meats were transferred to five floz plastic cups (King Ireland, Dublin, Ireland) and the surfaces covered with the cellophane. The cups were then moved to a refrigerator and stored at 4 C prior to analysis. 2.2. Aqueous solutions/suspensions of dry meat ingredients An initial screening study was conducted in which aqueous solutions/suspensions (5% w w
1) of typical dry ingredients (used in the formulation of meat products (Table 3)) were prepared by dissolving/dispersing weighed quantities of ingredients in 200 ml beakers with weighed quantities of distilled water. While the solutions/suspensions were being prepared they were stirred for 20 min using a mechanical stirrer (HB502, Bibby Sterilin LTD, UK) to aid homogeneity. A further experiment was conducted in which aqueous solutions/suspensions of ingredients were prepared at levels typical of those used in commercial meat product recipes (Table 4). The ingredients selected for this experiment were those which displayed very high or very

Table 2 A selection of publications listing dielectric property data for ingredients used in meat product manufacture Author

Freq (MHz)

Product and brief description of conditions

Roebuck and Goldblith (1972)

1000 and 3000

Potato starch in water, glucose, sucrose or glycerol-water solutions at 25 C (gelatinisation vs.) Chemically modified starches (degree of substitution and starch:water ratio vs.) Hydrated whey protein isolate, Ca-caseinate and wheat starch (alone or in combination) (temperature vs.) Six species of starch (30–95 C) Starch vs. salt mobility in solution Salt, D -sorbitol and sucrose solutions (21 C) Starch solutions (1-4% w w
1) (20–80 C) a-D -glucose solutions (10–60%) (0–70 C) Whey protein gel and liquid whey protein (20–121.1 C)

Miller, Gordon, and Davis (1991) Tsoubeli, Davis, and Gordon (1995) Ndife, Sumnu, and Bayindirli (1998) Bircan and Barringer (1998) Yaghmaee and Durance (2001) Piyasena, Ramaswamy, Awuah, and Defelice (2003) Liao, Raghavan, Dai, and Yaylayan (2003) Wang, Wig, Tang, and Hallberg (2003)

2450 2450 10, 20, and 30 2450 27, 40, 915, and 1800

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Table 3 Dry ingredients analysed in the present study Ingredient

Supplier

Butylated hydroxyanisole (BHA)

Lennox Laboratory Supplies Ltd, John F. Kennedy Drive, Naas Road, Dublin 12, Ireland

Sodium alginate Sodium benzoate Carrageenan (car-h-CHP1) Nitrate Nitrite Potato starch Sodium ascorbate Rusk White pudding seasoning Phosphate (P22) Salt Red2G Wheat gluten Monosodium glutamate (MSG) Natex grits Natex rusk Sodium sulphite anhydrous Soya concentrate Potassium sorbate

Wheat flour

Daniso Ingredients, Denmark William Blakes Ltd, Dublin, Ireland

RHM Foods Limited, Middlewich, Cheshire

Sample

Concentration (% w w
1)

Deionised water Sucrose Potato starch Wheat gluten Soy protein isolate Wheat flour Nitrite Carrageenan Potassium sorbate Sodium ascorbate Nitrate Phosphate (P22) White pudding spice Salt Salt

Not applicable 4 4 0.15 1 3 0.015 0.5 0.26 0.01 1.7 3 2.5 1.5 2.5

National Food Ingredients, Dock Road, Limerick, Ireland

Zhang et al. (2004). Subsequent calculation of power reflected (Pr), power transmitted (Pt), tan d and penetration depth (dp) was performed using the equations described in Zhang et al. (2004). Nutrinova, Nutrition Specialties and Food Ingredients GmbH, Industriepark Ho¨chst, 65926, Frankfurt, Germany Kerry Ingredients, Tralee Road, Listowel, Co. Kerry, Ireland

Caseinate Whey protein Soya protein isolate Glucanolactone Soya protein Sucrose

Table 4 Aqueous (deionised) solutions of ingredients prepared at concentrations representing typical usage levels in meat products

Schariau, Barcelona, Spain

low levels of dielectric activity in the initial screening study. 2.3. Preparation of lean beef dry ingredient blends From data acquired in aqueous solutions, the most and least dielectrically active ingredients were identified and blended with comminuted beef at levels corresponding to those present in a commercial recipe. Preparation of the meat blends was as described in Section 2.1 with the dry ingredients added to the beef prior to the blending procedure. 2.4. Measurement of dielectric properties at RF an MW frequencies Samples were equilibrated in an air-conditioned laboratory at 23 C (±1 C) and measurements were subsequently carried out using the methods described by

2.5. MW and RF cooking of meat batters 2.5.1. Sample preparation prior to MW and RF cooking Prior to MW or RF cooking each sample was removed from the chill and further blended for 30 s to ensure homogeneity and exclude pockets of air. To further prevent air inclusion and arcing, each blended sample was loaded into a 50 ml plastic syringe from which it was filled into a 100 ml glass beaker until it was level with the top of the beaker. The weight of each sample was recorded. Following this the beaker was immediately covered with cellophane and returned to the chill (4 C) for measurement on the following day. The following day each sample was taken from the chill, the cellophane was removed and its temperature was recorded using a ‘‘Digitron’’ 2046 T temperature probe (Eurolec Instrumentation, Dundalk, Louth, Ireland). Arcing during RF cooking was prevented by placing a glass plate (3 mm thick) on top of the beaker. This practice was also used during MW cooking of samples. 2.5.2. RF cooking RF cooking was carried out at 27.12 MHz using a Coaxial Power System Limited low power RF generator (Model No. RFG 600-27 Spectrum House, Finmere Road, Eastbourne, East Sussex, UK) with a complementary automatic impedance matching network and controller (Model No. AMN 600-27). These components were built into an RF oven supplied by Capenhurst Technologies, Chester, UK. The covered beaker was placed at the centre of the bottom electrode and

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the samples were cooked at 450 W for 90 s, after which they were immediately removed from the oven and their temperatures were recorded using the method described in Section 2.5.4 2.5.3. MW cooking MW cooking was carried out using an Amana Commercial MW (Model No. RS591SS, Amana Refrigeration Inc., P.O. Box 8901, IA 52204-0001, USA) which operated at a frequency of 2450 MHz. Similar to RF cooking, the power used to cook MW samples was 450 W. Each sample was individually taken from the chill and its temperature recorded using the temperature probe. The cellophane was removed and a glass plate was placed on top of the beaker to mimic conditions used in the RF cooking of samples and the samples were also cooked for a similar time of 90 s.

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wave moisture and methylene chloride fat extraction method (Bostian, Fish, Webb, & Arey, 1985). This was carried out using a CEM microwave moisture/solids analyser system (Model No. AVC-80, CEM Corporation, 3100 Smith Farm Road, Matthews, NC 28105, USA) and a CEM (Model No. FES-80) automatic fat extraction system. Protein analysis was carried out using a Leco (Model No. FP-428 Leco Corporation, 3000 Lakeview Avenue, St. Joseph, MI 49086-2396, USA) Nitrogen Protein Analyser using the method of Sweeney and Rexroad (1987). Ash was determined by heating in a furnace at 400 C for 4 h and weighing the residue. NaCl was determined by titration of the ash sample from the previous method, using the method of Kirk and Sawyer (1991).

3. Results and discussion 2.5.4. Temperature measurement following MW and RF cooking The temperature at 15 points within the cooked samples was recorded using a time temperature logger (Model No. 1250, Grant Instruments Ltd. Cambridge, England). A special wooden lid (thickness 1.9 cm) was designed to fit precisely on top of the beaker to minimise heat loss from the sample during temperature recording. Five pointed wooden pegs with three Type T thermocouples (Model No. M13 250C/T/Single/WnTip, Industrial Temperature Sensors, Dublin Ireland) fixed at the top centre and bottom were attached to the lid at the positions illustrated in Fig. 1. The overall mean temperature at the end of MW or RF cooking was compared. 2.6. Proximate analysis of meat A full proximate analysis (moisture, fat, protein, ash, and salt) was conducted on all meat used. Moisture and fat was determined by an automated, integrated micro-

3.1. Effect of frequency on dielectric properties Fig. 2 provides an illustration of the mean dielectric property values for the 42 materials under examination in the present study. When the overall average e 0 values are compared, e 0 had a similar order of magnitude across all three frequencies (i.e. 27.12, 915 and 2450 MHz). However, within frequencies e 0 values ranged from 7 to 82 depending upon the product. On average, the general trend was for e 0 values to decrease slightly with increasing frequency (Fig. 2) though there were exceptions to this in particular for solutions/suspensions with very high e00 (e.g. e 0 values for the 5% aqueous salt solution exhibited the opposite trend). When e 0 values within frequencies were compared an r2 of 0.98 was found between 915 and 2450 MHz e 0 values, though this r2 value was only 0.08 when 27.12 and 2450 MHz e 0 values were compared, with a similarly low correlation (r2 = 0.108) existing between 27.12 and 915 MHz. It

Fig. 1. Schematic diagram and photograph of thermocouple apparatus used to monitor meat temperature following RF or MW cooking (450 W, 90 s) in a 100 ml glass beaker.

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J.G. Lyng et al. / Meat Science 69 (2005) 589–602 ε’

27.12 MHz 915 MHz 2450 MHz

70

Pt 1

Pr

900

1

20

ε’’

Tan δ

150

dp (cm)

Fig. 2. Effect of frequency on the mean dielectric properties of products (note mean value of all meats and solutions used) measured in this study.

was not possible to attribute these low correlations between RF and MW e 0 values to a single factor. While fat had the lowest e 0 values at all frequencies it would appear that ionic ingredients (e.g. salt, white pudding spices (containing salt), nitrites etc.) have a depressing effect on e 0 values at 27.12 MHz which was not evident at MW frequencies. Another obvious difference was that the e 0 value of lean meats at 2450 MHz (average e 0 49.1 for lean) appeared to be depressed relative to that of the solutions, while at 27.12 MHz this depressing effect relative to the other solutions was not as evident (average e 0 of 71.8 for lean). Pr and Pt are derived exclusively from the e 0 value (Buffler, 1993) and as e 0 was broadly similar across all three frequencies it was not surprising that average values of Pr or Pt did not vary dramatically. Essentially higher e 0 values produce higher Pr values and lower Pt values. Therefore in general a slightly higher proportion of 27.12 MHz radiation is reflected. Similar to e 0 values, mean e00 values tended to decrease with increasing frequency, though unlike e 0 values the influence of frequency on the order of magnitude of e00 was particularly marked. e00 values at RF frequencies (i.e. 27.12 MHz average e00 of 805) were much greater than values at either of the MW frequencies (i.e. 915 MHz average e00 of 29 and 2450 MHz average e00 of 18). In spite of the large difference in the order of magnitude between MW and RF and in contrast to observations with e 0 values, r2 values of 0.99 and 0.97 were found between e00 values at 27.12 vs. 915 and 27.12 vs. 2450 MHz respectively. As shown by Engelder and Buffler (1991), calculating tan d involves dividing e00 by e 0 . As the order of magnitude for e 0 was not dramatically affected by frequency,

differences in tan d were largely determined by differences in e00 . Therefore the value of tan d for 27.12 MHz (average tan d 17.9) was much higher than its MW counterparts that were much lower and similar to each other (average tan d of 0.44 and 0.29 at 915 and 2450 MHz respectively). dp at 27.12 MHz was substantially higher (average dp of 121 cm) than 915 MHz (average dp of 9.8 cm), which in turn was higher than that of 2450 MHz (average dp of 2.6 cm) (Fig. 2). It is widely accepted that there is an inverse relationship between dp and frequency which is one of the reasons that 2450 MHz microwaves are used for domestic applications where product sizes are quite small whereas 915 MHz is more suitable for industrial applications. However, 27.12 MHz is the most suitable for application to large diameter products as illustrated by the dp results in the present study (Fig. 2). 3.2. Proximate analysis Proximate analysis results for the meats measured in the current study are presented in Table 5 which shows that the lean meat had broadly similar moisture (71.5– 74.5%), and ash (0.83–1.48) with turkey and chicken having slightly higher protein while beef, pork and lamb had slightly higher fat content. In contrast the pork fat had lower average moisture, ash, salt and protein and higher average fat. 3.3. A survey of the dielectric properties of lean meats and pork fat at 27.12 MHz 3.3.1. e 0 The e 0 values of all four lean meats were of similar order of magnitude with values ranging from 70.5 to 77.8 (Table 6). Ryyna¨nen (1995) reported that e 0 values measured at 2.8 GHz are largely a reflection of moisture content. In the present study lean meats had similar moisture contents and e 0 values. In contrast e 0 values and moisture contents of pork fat were substantially lower. When moisture content was correlated with e 0 value an r2 value of 0.99 was found when the results included pork fat though this reduced substantially to 0.06 when pork fat was excluded. This suggests that in contrast to the relationship between moisture and e 0 values at 2.8 GHz, (Ryyna¨nen, 1995), 27.12 MHz e 0 values are not strongly related to moisture content and would not be a reliable indicator of differences in moisture particularly if those differences are small. Other researchers have reported that lipids are generally inert dielectrically (Mudgett, Goldblith, Wang, & Westphal, 1977). Similar to observations on moisture content, r2 value of 0.99 were noted between e 0 value and fat content though when the pork fat was excluded from the data set this value decreased to 0.21. Therefore like moisture content, e 0 values at 27.12 MHz would not be a reliable indicator

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Table 5 Composition of meat used in the present study Species (anatomical location)

Type

Moisture (%)

Protein (%)

Fat (%)

Ash (%)

Salt (%)

Beef (forequarter trimmings) Lamb (leg) Pork (shoulder) Chicken (breast) Turkey (breast) Pork (back)

Lean Lean Lean Lean Lean Fat

71.5 73.0 73.9 73.6 74.5 19.0

21.3 21.9 20.1 24.3 24.1 3.9

6.1 3.6 4.4 1.2 0.4 76.1

0.83 1.48 1.13 0.86 0.98 0.20

0.11 0.14 0.08 0.13 0.08 0.07

Table 6 Dielectric properties (27.12 MHz) and temperature rises in meat used in the present study Species (anatomical location)

Type

e00

e0

dp (cm)

Tan d

Pr

DT

Beef (forequarter trimmings) Lamb (leg) Pork (shoulder) Chicken (breast) Turkey (breast) Pork (back)

Lean Lean Lean Lean Lean Fat

418.7 387.2 392.0 480.8 458.4 13.1

70.5 77.9 69.6 75.0 73.5 12.5

13.2 14.0 13.7 12.3 12.6 105.4

5.94 4.97 5.63 6.41 6.24 1.04

0.620 0.634 0.618 0.629 0.626 0.313

41.1 50.1 38.6 51.7 37.4 –

e00 : dielectric loss factor; e 0 : dielectric constant; dp: penetration depth; Pr: Power reflected; DT: Temperature rise (C) during heating @ 450 W for 90 s.

of small differences in fat content. Similar trends were noted between 27.12 MHz e 0 values and protein content, with strong relationships where differences were large and poor relationships when differences were small. 3.3.2. e00 e00 values for lean meats were ranked in the following order lamb < pork < beef < turkey < chicken though pork fat was dramatically lower than all lean meats (Table 6). Similar to observations on e 0 , high r2 values (>0.96) were obtained when correlations were made between moisture, fat and protein contents of all meat (i.e. lean and fat) and e00 . However, when results for pork fat were excluded, the r2 values dropped substantially suggesting again that when differences in these composition attributes were large, strong relationships occurred with 27.12 MHz e00 values. However, when the magnitude of these differences in composition is small, e00 at 27.12 MHz could not be used as a reliable indicator of relative differences in protein, fat and moisture content. 3.3.3. Tan d Differences in tan d values (calculated as a ratio between e00 and e 0 ) for the lean meats were also noted with lean pork having lower values than the other lean meats while pork fat was again much lower than all the lean meats (Table 6). When attempts were made to relate the differences in tan d to differences in composition, similar to observations in e 0 and e00 strong relationships (as indicated by r2 values >0.94) were found when pork fat was included to give a broad range of moisture, fat and protein contents. However, when pork fat results were excluded, r2 values of less than 0.4 were recorded.

3.3.4. dp dp is related to the amount of power absorption that occurs as the RF radiation passes through the product. As 27.12 MHz energy penetrates and passes through a product more and more of it is absorbed and the field strength decreases with increasing distance from the surface. As expected a strong inverse relationship was recorded between e00 and dp (r2 > 0.96). For meats with higher e00 values (e.g. chicken and turkey), more of the energy is absorbed in the other regions of the product with less available to penetrate deeper into the product. Thus in such products dp values are slightly lower (Table 6). On the other end of the spectrum, for pork fat with very low e00 values, dp values are very high indicating that 27.12 MHz radiation passes though the fat and is not absorbed. Again, similar to e 0 , e00 and tan d high r2 values were noted between dp and moisture, protein or fat when the range of these values was high (i.e. when lean and fat were combined), but when the range was reduced due to the exclusion of pork fat the r2 values also reduced. 3.3.5. Pr As Pr is related to e 0 pork fat the lowest Pr, and lamb the highest. As for the aforementioned dielectric properties, good correlations were noted with composition attributes when the range of composition was high (i.e. when lean and fat were combined) but reduced substantially when the composition range decreased due to the exclusion of pork fat. 3.3.6. Temperature rise It was not possible to heat fat in the RF oven used in the present study as the oven would not tune. This was most likely due to the low e 0 and e00 values of the fat. No trends were evident in the magnitude of the temperature

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were reduced substantially with protein having an r2 of 0.82 and moisture and fat having r2 values of less than 0.4.

rises recorded within the lean meat heated at this frequency (Table 6) suggesting that the magnitude of the composition differences were not sufficient to affect temperature increases assessed by the method used.

3.4.4. dp Similar to observations at 27.12 MHz pork fat had an extremely large dp value compared to the lean meats, which had similar results but were much less than the values recorded at 27.12 MHz (Table 7), which indicated that RF power is suitable for large diameter foods compared to MW. When correlations with composition were conducted, high r2 values were noted for moisture, protein and fat (all r2 > 0.96) while these values reduced when pork fat was excluded (r2 of 0.61, 0.77 and 0.94 respectively for moisture, protein and fat). These correlations reflect to a large extent the observations for e00 .

3.4. A survey of the dielectric properties of lean meats and pork fat at 2450 MHz 3.4.1. e 0 e 0 values varied with turkey having the highest and beef having the lowest e 0 of the lean meats assessed with pork fat having a much lower e 0 values than all other meats (Table 7). When moisture content is correlated with e 0 , an r2 value of 0.97 was found at 2450 MHz and while a slight reduction in r2 occurred when pork fat was excluded (r2 = 0.89) the magnitude of the reduction was not comparable with the large reduction which occurred at 27.12 MHz. This is in agreement with observations of Ryyna¨nen (1995) who noted that at a similar frequency (2.8 GHz), e 0 is largely a reflection of moisture content. While differences in protein, fat ash and salt also occurred when pork fat data was excluded from the data set the magnitude of the correlations with these values was very low.

3.4.5. Pr Pr values for lean meats were broadly similar and were higher than that observed in pork fat (Table 7). Trends in the relationship between Pr and composition were largely in line with those reported for e 0 due to the strong relationship between this value and e 0 . 3.4.6. Temperature rise Pork back fat exhibited little electrical polarity (as indicated by its dielectric property data) and therefore could be expected to receive less energy directly from the MW radiation compared to lean meats. However, when the temperature rise of standard quantities of lean and fat are compared after heating for a standard time, temperature rises in the fat were much higher than in the lean (Table 7). Fat has a lower specific heat capacity compared to water (Lewis, 1987) and therefore the higher temperature of the fat can largely be attributed to its lower specific heat capacity which although it absorbs less MW energy (as indicated by its lower e00 (Table 7)), it requires less per unit mass for a specified temperature rise.

3.4.2. e00 The e00 values of turkey and chicken were highest and while beef was lowest of the lean and pork fat was lowest overall (Table 7). These differences are largely attributable to compositional differences. Strong correlations were noted (r2 > 0.96) between e00 and moisture, protein and fat when pork fat with its substantially differing composition was included. When pork fat was excluded from the data set r2 values between composition and e00 remained relatively high at 0.79, 0.88 and 0.52 for moisture, fat and protein respectively. For the meat products examined, increasing moisture and protein content increased e00 while an increase in fat content reduced e00 .

3.5. A survey of the dielectric properties of aqueous solutions/suspensions containing non-meat ingredients at a standard level of 5%

3.4.3. Tan d The tan d values of the lean meats were broadly similar while tan d of pork fat was much lower due to the lower ratio between e00 and e00 (Table 7). When tan d of all meats were correlated with moisture, protein and fat contents, strong correlations were observed (all r2 > 0.98) though when pork fat was excluded r2 values

3.5.1. Dielectric properties at 27.12 MHz Survey results on the dielectric properties of 5% (w w
1) aqueous suspensions/solutions at 27.12 MHz

Table 7 Dielectric properties (2450 MHz) and temperature rises in meat used in the present study Species (anatomical location)

Type

e00

e0

dp (cm)

Tan d

Pr

DT

Beef (forequarter trimmings) Lamb (leg) Pork (shoulder) Chicken (breast) Turkey (breast) Pork (back)

Lean Lean Lean Lean Lean Fat

13.7 15.0 15.1 16.1 18.0 0.76

43.7 49.4 51.3 49.0 56.3 7.9

1.91 1.85 1.86 1.72 1.64 14.55

0.313 0.303 0.295 0.328 0.320 0.095

0.543 0.563 0.570 0.562 0.585 0.227

61.2 72.6 55.1 65.0 68.3 90.1

e00 : dielectric loss factor; e 0 : dielectric constant; dp: penetration depth; Pr: Power reflected; DT: Temperature rise (C) during heating @ 450 W for 90 s.

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are presented in Table 8. While there were differences in e 0 these differences were small by comparison with the differences in e00 and therefore the data in Table 8 is ranked in ascending order according to e00 . As expected deionised water has the lowest e00 value of all the solutions/suspensions analysed. However, sucrose, starch and the antioxidant BHA also had extremely low e00 values. At the other end of the scale solutions such as those containing nitrate, nitrite and salt had e00 values which were up to four orders of magnitude higher than deionised water which also reflected in the tan d values. This would be expected as such ionic compounds would be completely dissociated in water. Relative to the e00 of lean meats assessed (e00 ranging from 387 to 480.8) the table can be subdivided into two groups one of which (deionised water – sodium alginate) had lower e00 values than lean and the other (MSG – Salt) which had higher e00 values than the lean. Conversely the dp (cm) values for solutions with high e00 are low relative to those of deionised water and other solutions with low e00 values. While some differences in e 0 were evident, it was difficult to relate these differences to chemical composition, as all e 0 values were of a similar Table 8 Dielectric properties (27.12 MHz) of 5% aqueous solutions/suspensions of selected ingredients Ingredient

e00

e0

dp (cm)

Deionised water Sucrose Potato starch Antioxidant BHA Boiled potato starch Wheat gluten Wheat flour Caseinate Whey protein Natex rusk Soya protein isolate Soya concentrate Natex grits Gluconolactone Soya protein Rusk Carrageenan Sodium alginate MSG Sodium ascorbate Red 2G Sodium benzoate Potassium sorbate Phosphate (P22) Sodium sulphite anhydrous White pudding spice Nitrate Nitrite Salt

0.88 1.43 3.82 4.01 6.32 39.3 44.6 89.2 96.0 121 123 127 143 162 177 180 205 379 842 880 992 1158 1639 1968 2864

79.7 75.8 78.0 64.8 69.5 77.4 52.9 81.2 80.4 74.9 80.7 82.6 77.8 75.2 77.9 76.9 81.0 78.5 77.2 67.2 72.4 69.0 61.3 56.4 43.0

3535 2143 814 707 465 81 62 40 37 30 31 30 27 25 23 23 21 14 9.0 8.7 8.2 7.5 6.3 5.7 4.7

3037 3299 4065 5178

34.1 59.7 47.5 22.5

4.5 4.4 3.9 3.5

Tan d 0.011 0.019 0.049 0.062 0.091 0.508 0.843 1.10 1.19 1.62 1.52 1.54 1.84 2.15 2.27 2.34 2.53 4.83 10.9 13.1 13.7 16.8 26.7 34.9 66.6 89.2 55.3 85.7 230.6

Pr 0.63 0.63 0.63 0.61 0.62 0.63 0.57 0.64 0.64 0.63 0.64 0.64 0.63 0.63 0.63 0.63 0.64 0.64 0.63 0.61 0.62 0.62 0.6 0.59 0.54 0.5 0.59 0.56 0.42

e00 : dielectric loss factor; e 0 : dielectric constant; dp: penetration depth; Pr: Power reflected.

597

order of magnitude which was also the case with Pr values. 3.5.2. Dielectric properties at 2450 MHz Similar to the trend observed at 27.12 MHz, solutions/suspensions containing ingredients with little or no ionic content (e.g. deionised water, antioxidant BHA etc.) had very low e00 values whereas solutions containing high ionic ingredients (e.g. nitrate, nitrite and salt) had relatively large e00 values (Table 9). However, relative to the results at 27.12 MHz, the degree of variation between ionic and non-ionic solutions/suspensions was relatively small, with only one order of magnitude in variation being observed. Similar to observations at 27.12 MHz the 5% solutions can be subdivided into two groups based on their e00 values relative to lean meats (e00 ranged from 13.7 to 18.0). Interestingly while the relative ranking at the two frequencies was not the same, the make up of the groups of ingredients having lower and higher e00 values than lean meat was identical to that observed at 27.12 MHz. This again most likely reflects the ionic content with the low e00 range having a lower ionic content than meat and the high e00 range having a higher ionic content than lean meat. Table 9 Dielectric properties (2450 MHz) of 5% aqueous solutions/suspensions of selected ingredients Ingredient

e00

e0

dp (cm)

Tan d

Pr

Deionised water Antioxidant BHA Soya concentrate Natex rusk Potato starch Natex grits Wheat flour Boiled potato starch Sucrose Caseinate Whey protein Soya protein isolate Rusk Wheat gluten Soya protein Gluconolactone Carrageenan Sodium alginate Sodium ascorbate Red 2G MSG Sodium benzoate Potassium sorbate Phosphate (P22) White pudding spice Sodium sulphite anhydrous Nitrate Nitrite Salt

6.9 7.1 7.3 7.5 8.3 9.0 9.1 9.2 9.4 9.9 10.2 10.2 10.3 10.3 10.9 11.5 11.6 13.6 18.7 21.2 23.2 24.9 30.1 34.4 42.8 44.7 44.9 53.1 65.5

76.8 68.4 43.3 47.9 77.8 57.7 74.4 76.1 76.1 74.3 74.2 75.9 77.2 74.5 76.3 76.1 76.8 76.1 74.1 72.7 74.5 73.1 74.1 73.8 71.2 70.7 70.9 69.6 67.3

5.0 4.5 3.5 3.6 4.2 3.3 3.7 3.7 3.6 3.4 3.3 3.3 3.3 3.3 3.1 3.0 2.9 2.5 1.8 1.6 1.5 1.4 1.1 1.0 0.80 0.77 0.76 0.65 0.53

0.090 0.104 0.169 0.157 0.106 0.156 0.122 0.121 0.124 0.133 0.137 0.134 0.133 0.139 0.143 0.151 0.152 0.178 0.253 0.291 0.311 0.340 0.407 0.467 0.602 0.632 0.633 0.763 0.973

0.63 0.62 0.54 0.56 0.63 0.59 0.63 0.63 0.63 0.63 0.63 0.63 0.63 0.63 0.63 0.63 0.63 0.63 0.63 0.62 0.63 0.63 0.63 0.63 0.62 0.62 0.62 0.62 0.61

e00 : dielectric loss factor; e 0 : dielectric constant; dp: penetration depth; Pr: Power reflected.

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Another difference between dielectric properties of the solutions at 27.12 vs. 2450 MHz is the order of magnitude of the dp values which were substantially higher at 27.12 MHz especially for non-ionic meat ingredients at 27.12 MHz. Similar to that at 27.12 MHz, variations in e 0 at 2450 MHz were smaller than those observed for e00 and this influence is also evident in Pr values at this frequency. 3.6. A survey of the dielectric properties of aqueous solutions/suspensions containing selected non-meat ingredients at typical industrial usage levels While measuring the dielectric properties of the meat ingredient at a standard level of 5% (Section 3.4) is useful for ranking the relative dielectric properties of typical meat ingredient, a level of 5% would not be a good reflection of the typical levels many of these ingredients would be used at in the manufacture of meat and meat products. Therefore the objective of this part of the study was to measure the dielectric properties of a selected range of typical non-meat ingredients which were identified (Section 3.4) as having very low or very high e00 values. Aqueous solutions/suspensions of these ingredients were prepared at levels representative of their normal commercial usage levels and their dielectric properties are listed in Tables 10 and 11. 3.6.1. Dielectric properties at 27.12 MHz As noted previously (Section 3.4) aqueous solutions/ suspensions containing essentially non-ionic meat ingredients had the lowest e00 values (Table 10). For ingredients such as nitrites and nitrates which were ranked second and third highest for e00 when measured at the 5% level (Section 3.4), Table 10 shows the influence of these ingredients on e00 at their typical usage levels is substantially reduced particularly for nitrite which is used at

a very low level (0.015%). Salt remains the ingredient with the highest e00 values even at the lower usage level of 1.5%. However, when the magnitude of the difference between e00 values of salt and phosphate are compared at typical usage levels (e.g. 1.5% vs. 3% w w
1 respectively) the magnitude of the difference between them is substantially less (Table 10) than the difference observed at the 5% level (Table 8). In contrast to observations on 5% solutions, nitrite, potassium sorbate and sodium ascorbate had lower e00 than lean meats due to their low usage levels. Similar to the trends observed at the 5% level (Table 8), the magnitude of the variation in dp (cm) was large between ingredients with high vs. low e00 values (e.g. dp for deionised water was 707 times higher than the values for the 2.5% salt solution). Similar to previous observations at 27.12 MHz at the 5% level (Section 3.4.1), the magnitude of the variation in e 0 was small relative to that for e00 and this was also reflected in the Pr values. 3.6.2. Dielectric properties at 2450 MHz The relative ranking of e00 at 2450 MHz was identical to that at 27.12 MHz with the exception of wheat flour which was ranked slightly higher at 2450 MHz. (Table 11). In contrast to observations for 5% solutions, though in complete agreement with observations at 27.12 MHz, nitrite, sodium ascorbate and potassium sorbate had lower e00 than lean meat, with nitrates, phosphate, white pudding spice having higher e00 than lean meat. Similar to observations for the 5% solutions, the magnitude of variation of e00 was relatively small when compared to that observed at 27.12 MHz. Trends for e 0 , dp, tan d, and Pr were similar to those reported at 27.12 MHz (Section 3.5.1). Overall, results for e00 of 1.5%, 2.5% and 5% salt solutions at 27.12 and 2450 MHz (Tables 8–11) suggest a linear relationship between salt concentration and e00

Table 10 Dielectric properties (27.12 MHz) of aqueous solutions/suspensions of key meat ingredients at typical industrial usage percentages Sample ID

% (w w
1)

Deionised water Sucrose Potato starch Wheat gluten Soy protein isolate Wheat flour Nitrites Carrageenan Potassium sorbate Sodium ascorbate Nitrates Phosphate (P22) White pudding spice Salt Salt

NA 4 4 0.15 1 3 0.015 0.5 0.26 0.01 1.7 3 2.5 1.5 2.5

e00 0.88 1.01 1.32 1.49 26.24 29.83 32.00 35.32 100.7 230.5 1197 1236 1382 1511 2514

e0 79.7 77.1 77.0 76.7 78.1 76.5 75.0 78.9 77.1 77.3 76.2 74.7 69.1 73.6 67.5

e00 : dielectric loss factor; e 0 : dielectric constant; dp: penetration depth; Pr: Power reflected.

dp (cm) 3535 3064 2334 2074 120 105 97 91 35 19 7.4 7.3 6.9 6.6 5.0

Tan d

Pr

0.011 0.013 0.017 0.019 0.335 0.390 0.427 0.447 1.307 2.982 15.700 16.554 20.002 20.54115 37.22471

0.63 0.63 0.63 0.63 0.63 0.63 0.63 0.64 0.63 0.63 0.63 0.63 0.62 0.63 0.61

J.G. Lyng et al. / Meat Science 69 (2005) 589–602

599

Table 11 Dielectric properties (2450 MHz) of aqueous solutions/suspensions of key meat ingredients at typical industrial usage percentages Sample ID

% (w w
1)

e00

e0

dp (cm)

Tan d

Pr

Deionised water Potato starch Wheat gluten Sodium ascorbate Soy protein isolate Carrageenan Nitrite Sucrose Potassium sorbate Wheat flour Nitrates Phosphate (P22) White pudding spice Salt Salt

NA 4 0.15 0.01 1 0.5 0.015 4 0.26 3 1.7 3 2.5 1.5 2.5

6.9 8.73 8.75 9.05 9.14 9.26 9.80 10.02 10.37 11.01 21.90 25.46 25.87 26.19 36.37

76.8 77.2 77.1 77.5 77.0 77.1 76.1 75.7 77.2 78.0 74.6 74.4 73.8 73.6 71.8

4.95 3.92 3.91 3.79 3.74 3.70 3.47 3.39 3.31 3.14 1.55 1.34 1.31 1.30 0.93

0.090 0.113 0.113 0.116 0.118 0.120 0.129 0.132 0.134 0.141 0.294 0.342 0.351 0.356 0.507

0.63 0.63 0.63 0.63 0.63 0.63 0.63 0.63 0.63 0.64 0.63 0.63 0.63 0.63 0.62

e00 : dielectric loss factor; e 0 : dielectric constant; dp: penetration depth; Pr: Power reflected.

(r2 = 0.9998 and 0.9992 at 27.12 and 2450 MHz respectively) though further work would be required to confirm this relationship over a broader range of salt concentrations. However, in the context of meat processing 5% would be substantially higher than the maximum salt concentration ever likely to be used in a meat product.

in typical meat products. In addition pork fat has been shown to have a low e00 value, while water is also important as a dipolar molecule which acts a medium for ionic solvation. 3.7.1. Dielectric properties and temperature rises of beef/ ingredient blends at 27.12 vs. 2450 MHz Tables 12 and 13 show dielectric properties (27.12 and 2450 MHz) and temperature rises for beef blended with a selection of added ingredients with results sorted according to e00 . For the most part e00 values of the meat blends were a reflection of the e00 values of the nonmeat ingredients in aqueous suspensions. Therefore the additions of ingredients such as salt, phosphate and nitrite (which have high e00 values in aqueous suspensions) also resulted in meat blends with high e00 values. The opposite was true for ingredients such as starch and gluten which had low e00 values in aqueous suspensions though this was not the case for added water which appeared to have no effect or even slightly elevate the e00 values of the beef to which it was added. It must be noted that all other added ingredients in Tables 12 and 13 are essentially dry ingredients, while water is a liquid and therefore can act as a solvent for other ionic components present in meat. Fat also

3.7. Influence of incorporation of selected ingredients on the dielectric properties and temperature rises of beef blends Selection of ingredients was based on their dielectric properties (as assessed in Sections 3.4, 3.5) in conjunction with their typical incorporation levels in meats. Salt and phosphate were chosen due to their high e00 ranking as discussed in Section 3.4, 3.5. Nitrite was chosen as this ingredient is an ionic compound with the potential to influence e00 , though at the typical levels used in meat products, its influence was not known. Starch and gluten were chosen as they have low e00 values in aqueous suspensions, though starch is included at relatively high levels (up to 4%) while gluten is generally added at low levels (e.g. 0.15%). Pork fat and water were also selected as they are major ingredients

Table 12 Dielectric properties (27.12 MHz) and temperature rises of beef muscle blends with added ingredients Ingredient

Level added (%)

e00

e0

dp (cm)

Tan d

Pr

DT

Pork fat Potato starch Gluten No additives Water Nitrite Phosphate (P22) Salt

20 4 0.15 NA 25 0.015 3 1.5

259.6 375.5 375.6 396.2 399.5 408.1 851.4 1150.3

55.7 71.1 67.4 71.6 77.0 74.5 78.2 69.5

18.3 14.2 14.1 13.8 13.7 13.6 9.0 7.6

4.617 5.301 5.582 5.534 5.19 5.485 11.21 16.57

0.58 0.62 0.61 0.62 0.63 0.63 0.63 0.62

31.8 38.4 38.4 40.4 44.1 31.6 30.2 22.1

e00 : dielectric loss factor; e 0 : dielectric constant; dp: Penetration depth; Pr: power reflected; DT: Temperature rise (C) during heating @ 450 W for 90 s.

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Table 13 Dielectric properties (2450 MHz) and temperature rises of beef muscle blends with added ingredients Ingredient

Level added (%)

e00

e0

Tan d

dp (cm)

Pr

DT

Pork fat Potato starch Gluten No additives Nitrite Water Phosphate (P22) Salt

20 4 0.15 NA 0.015 25 3 1.5

12.1 14.7 15.5 15.6 15.6 15.8 22.1 24.4

40.6 47.5 49.4 50.8 50.6 56.0 48.3 47.8

0.297 0.309 0.316 0.306 0.308 0.284 0.456 0.509

2.1 1.9 1.8 1.8 1.8 1.9 1.3 1.1

0.53 0.56 0.56 0.57 0.57 0.58 0.56 0.56

68.2 71.1 69.0 61.4 61.6 55.4 65.1 58.1

e00 : dielectric loss factor; e 0 : dielectric constant; dp: penetration depth; Pr: Power reflected; DT: Temperature rise (C) during heating @ 450 W for 90 s.

had a negative effect on e00 due to a combination of its low e00 and also the fact that it is an ingredient added at a high level of 20%. It should be noted that the beef used for this experiment was purchased separately from the beef used in the earlier work and hence the slight differences in dielectric properties are most likely due to slight differences in composition. When Tables 12 and 13 are compared it is apparent that similar to results found in aqueous solutions/suspensions (Tables 10–13), e00 values at 27.12 MHz were considerably greater than those at 2450 MHz. Therefore the influence of e00 is very evident in the magnitude of tan d values which are substantially higher at 27.12 MHz vs. 2450 MHz. It is also apparent that within each frequency the magnitude of the e00 for ingredients in the blend is related to the magnitude of their values in aqueous suspensions/solutions. Similar to e00 results, dp values at 27.12 MHz were higher than those at 2450 MHz. In addition as previously observed dp values were inversely related to e00 results. e 0 and Pr were of a similar order of magnitude at both 27.12 and 2450 MHz. Although identical power levels (450 W) and cooking times (90 s) were used, the average DT values at 27.12 MHz were 34.7 C compared to the average DT at 2450 MHz of 63.7 C. It is worth noting that a standardised sample size was also used (100 ml glass beaker 5 cm diameter · 6.8 cm height). As microwaves at 2450 MHz approach the product from all directions, the maximum distance a microwave approaching the product from the side would have to penetrate to reach the centre would be 2.5 cm and this value is closely in line with the magnitude of the dp values at 2450 MHz (average 1.7 cm). In contrast RF heating at 27.12 MHz occurs in a directional manner between parallel electrodes. The mean dp value for the samples at 27.12 MHz was 13 cm. However, the sample geometry used in the present case would not be representative of the majority of meat product sizes encountered on a commercial scale. Therefore the larger dp values encountered at 27.12 MHz would be more suited to producing a uniformly heated large diameter product.

4. Conclusion This work illustrated the influence of frequency on the dielectric properties of meat products and aqueous solutions of typical ingredients used in meat product manufacture. As a general rule for most of the meats and ingredients measured, e 0 and Pr and more noticeably e00 , tan d, and dp tend to decrease with increasing frequency while Pt tends to increase with increasing frequency, though there were some exceptions to this. Proximate composition also had an effect on dielectric properties though at 27.12 MHz correlations between dielectric properties (i.e. e 0 , e00 , tan d, dp, and Pr) and selected proximate attributes (such as moisture, fat and protein) tended only to be strong only when the compositional attributes varied across a broad range. In contrast at 2450 MHz, strong correlations were noted across narrower composition ranges, particularly between e 0 vs. moisture, e00 vs. moisture, fat and to a lesser extent protein, tan d vs. protein and also dp vs. moisture, protein or fat. This suggests that MW dielectric properties are more sensitive to composition which could have potential as rapid method for assessing meat composition. At both 27.12 and 2450 MHz, e00 of 5% aqueous solutions/suspensions showed an identical subdivision into a group which had lower e00 than lean meats and a group which had higher e00 values than the lean meats which could most likely be attributed to the ionic content of the ingredients relative to that of lean meat. However, when ingredient solutions were prepared at levels representing normal usage levels, a number of ingredients which had higher e00 values than lean meat when prepared at 5% level dropped below lean meat due to their low usage levels. Finally when blends of beef containing selected ingredients which had low and high e00 values (added at low or high levels as appropriate) were compared to lean meat to which no ingredients were added, pork fat, potato starch and gluten reduced e00 while water, nitrite, phosphate and salt increased e00 . These changes in e00 did not correlate well with observed temperature rises (DT) suggesting the importance of thermal properties (e.g. specific heat capacity) in addition to dielectric properties in determining actual temperature rises in products.

J.G. Lyng et al. / Meat Science 69 (2005) 589–602

Acknowledgements This research has been part-funded by grant aid under the Food Institutional Research Measure, which is administered by the Department of Agriculture, Food and Rural Development, Ireland. Thanks are given to Mr. Niall OÕBrien for his help in the preparation of samples.

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