Food Chemistry 159 (2014) 293–301

Contents lists available at ScienceDirect

Food Chemistry journal homepage:

Assessment of heat treatment of various types of milk Lambros Sakkas, Alexandra Moutafi, Ekaterini Moschopoulou, Golfo Moatsou ⇑ Laboratory of Dairy Research, Department of Food Science and Human Nutrition, Agricultural University of Athens, Iera Odos 75, 11855 Athens, Greece

a r t i c l e

i n f o

Article history: Received 10 December 2013 Received in revised form 19 February 2014 Accepted 5 March 2014 Available online 14 March 2014 Keywords: Heat treatment b-Lactoglobulin a-Lactalbumin Lactulose Furosine Milk Condensed milk Milk powders

a b s t r a c t Raw milk (RM), reconstituted condensed milk (CM) and three types of reconstituted milk powders (SMPs) were heated indirectly at 80–140 °C for 4 s. Native b-lactoglobulin after 90 °C treatment of RM was 1132 ± 167 mg/L but no reliable quantities were estimated at temperatures >100 °C, whereas 218 ± 43 mg/L residual a-lactalbumin were found at 130 °C. Average lactulose contents from 51 to 1549 mg/L were detected at P100 °C; average furosine was 1.9 and 126.5 mg/L in raw and 140 °C treated milks respectively. The behaviour of heated CM was similar to that of heated RM except for higher furosine concentration. Reconstituted SMPs contained high quantities of lactulose and furosine, the ratio of which was lower than in similarly treated RM. Among the market milks analysed, the group of high-pasteurised milks was highly variable; i.e. native b-lactoglobulin was 69–2831 mg/L, lactulose 0–824 mg/L and furosine 3.3–68.8 mg/L. Ó 2014 Elsevier Ltd. All rights reserved.

1. Introduction The production of heat treated milk for human consumption covers the spectrum from pasteurisation to in-container sterilisation with respect to the shelf life and the heat-induced changes of milk. The efficacy and the effects of heat treatments are related to the temperature–time combinations, heating method utilised and milk pre-treatment conditions (Walstra, Wouters, & Geurts, 2006). Between the two well-known categories of drinking milk, i.e. (low) pasteurised and UHT milk, there is the peroxidase negative extended shelf life (ESL) milk, marketed in several countries as high-pasteurised milk. It can be stored up to 60 d under refrigerated conditions, while its flavour is expected to be similar to pasteurised milk. Various processing and packaging technologies are combined for the production of ESL milk, i.e. 130–145 °C for 65 °C, unfolding of b-lg, i.e. first stage of denaturation, occurs. According to Claeys, Ludikhuyze, Van Loey, and Hendrickx (2001a), denaturation follows first order kinetics with z-values of 7.9 °C (D75°C = 49.9 min) from 70–80 °C and z-values of 24.2 °C (D85°C = 3.53 min) from 83–90 °C. Cystine disulphide bonds disrupt and along with the free sulfhydryl group of the native molecule are available to participate in thiol/disulfide exchanges; they react intra- or inter-molecularly mainly with j-casein on the micelle surface and with proteins on milk fat globule membrane (MFGM). The main result of this reaction is the formation of b-lg/j-casein complexes, which are a characteristic feature of heat-treated milks. At higher temperatures, i.e. between 70 and 96 °C, denaturation of a-la takes place that forms complexes with aggregates of b-lg. Denatured a-la forms also complexes with as2-casein and with MFGM at high temperatures (Considine, Patel, Anema, Singh, & Creamer, 2007; Corredig & Dalgleish, 1996; Jeanson, Dupont, Grattard, & Rolet-Répécaud, 1999). Several studies on residual native whey protein content of heattreated milk have been carried out (e.g., Corzo, Delgado, Troyano, & Olano, 1994a; Corzo, López-Fandiño, Delgado, Ramos, & Olano, 1994b; Elliott, Datta, Amenu, & Deeth, 2005; Elliott et al., 2003; Feinberg, Dupont, Efstathiou, Louâpre, & Guyonnet, 2006; Jeanson et al., 1999; Lorenzen et al., 2011; Mayer, Raba, Meier, & Schmid, 2010; Morales, Romero, & Jiménez-Pérez, 2000; Villamiel, Arias, Corzo, & Olano, 1999; Villamiel, López-Fandiño, Corzo, & Olano, 1997). According to them, residual acid soluble b-lactoglobulin (b-lg) content of low pasteurised milks ranges from 1606 to 4140 mg/L, of ESL milk from 140 to 3680 mg/L, of UHT-direct heating method (UHT-DM) milk from 150 to 1120 mg/L, of UHT-indirect method (UHT-IM) milks is 1.5 mg and high-heat when WPN 6 1.5 mg N/g. Therefore, according to the WPN, the b-lg and a-la contents of LH-SMP were expected to be lower than that of MHSMP, opposite to the findings in Table 1. LCT was detected in all three types of untreated reconstituted SMPs. In non-treated HHSMP, the LCT content was in accordance with the previously mentioned pre-heating conditions; these values corresponded to 130 °C RM treatments (Table 1). The non-treated reconstituted SMPs contained considerable amounts of FRS (Table 1). Resmini and Pellegrino (1993) report that 100–400 mg FRS per 100 g of protein are typical for SMPs, and that >600 mg/100 g of protein can be detected after a long storage period. It is attributed to low aw during spray drying that favours the evolution of Maillard reaction during storage even if the treatment conditions were not favourable for LCT formation. Consequently, the LCT/FRS ratio of SMPs treated at 130 °C was much lower compared to similarly treated RM and CM (Table 1). 3.2. Market milk samples The results for the group of market milks (paragraph 2.1) are presented in Table 2. Thermisized milk (TM) contained 3539 ± 175 mg/L native b-lg close to the 3800 mg/L in thermalised milks analysed by Morales et al. (2000). Lower values, 3156 ± 116 and 3350 ± 115 mg/L, were found in LP/FF and LP/LF milks, respectively, which can be also attributed to standardisation of milk composition apart from possible heat denaturation; apparently the higher content of LF milk is due to its higher total protein content. These values were within the range of values for LP market milks reported by Jeanson et al. (1999), Villamiel et al. (1999), and Mayer et al. (2010), and close to those of Birlouez-Aragon et al. (1998), and Feinberg et al. (2006). In the study of Lorenzen et al. (2011), six LP milk samples taken from dairy factories contained from 3302 to 4745 mg/L acid soluble b-lg, whereas in the study of Mayer et al. (2010), a great variability was depicted in LP market milks, i.e. the native b-lg content of 33 market samples ranged from 2528 to 3799 mg/L. Considering the average b-lg content of raw milk at 3300–3500 mg/L, the lowest value for pasteurised milk can be 2600 mg/L, for high pasteurised milk 2000 mg/L and for UHT milk 50 mg/L, as cited by Claeys et al. (2002b), and Mayer et al. (2010). The latter group recommends an acid soluble b-lg content of 1800 mg/L as an upper heating limit for ESL milk. The UHT milks’ native b-lg content was, as expected, low in accordance to the results of experimental milks of Table 1. The native b-lg content of HP/ESL milks of Table 2 varied considerably. Bearing in mind the abovementioned limits, only 26 samples out of 63 fulfilled the limits of P1800 mg/L, that is 41% of the total. Among them, the MF + LP milk was close to LP milks, similar to the findings of Lorenzen et al. (2011); on the contrary

28% of these milks had residual native b-lg 6500 mg/L, which is consistent with UHT milk. Great variability for this type of market milk from 790 to 2600 mg/L has been also reported by Villamiel et al. (1999), and by Mayer et al. (2010), who report that the acid-soluble b-lg content of 71 ESL milks from 17 brands was from 140 to 3679 mg/L and that 55% of ESL samples contained 1800 mg/L residual native b-lg. The absence of detectable LCT in the HP/LL samples contrasts with their very low b-lg content; it is due to very low initial concentrations of lactose, indicating that LCT is not a proper index for LL milks. LCT content in the majority of UHT milks was within the 100–600 mg/L range reported for this category (Claeys et al., 2002b). Samples of product 3 could be characterised as sterilised milk. Moreover, according to the >100 mg/L limit, a considerable amount of HP/ESL samples could be characterised as UHT, as happened also with their residual acid-soluble b-lg. Nevertheless, Table 2 indicates that LCT was not detected in samples with residual b-lg >1800 mg/L. There are several reports about the estimation of LCT content of market milks by HPLC. Birlouez-Aragon et al. (1998) and Jeanson et al. (1999) did not detect any LCT in pasteurised milks, in contrast to Feinberg et al. (2006), who reported 15 ± 12.1 mg/L LCT for milk heated at 74 °C for 30 s. Birlouez-Aragon et al. (1998) did not detect LCT in HP milks, whereas Feinberg et al. (2006) report 31 ± 13.6 mg/L. In UHT-IM LCT was about 400 mg/L (Feinberg et al., 2006), 460 mg/L (Elliott et al., 2005), 550 mg/L (Birlouez-Aragon et al., 1998) or in the range 543–650 mg/L (Cattaneo et al., 2008). FRS upper limits cited by Claeys et al. (2002) and Mayer et al. (2010) are 8 mg/100 g protein for pasteurisation, 20 mg/100 g protein for high pasteurisation and 250 mg/100 g protein for UHT process. Fourteen representative samples were analysed with regard to their FRS content (Table 2). The FRS contents of analysed TM, LP and MF + LP samples were higher than that of RM in Table 1, but within the abovementioned limits for pasteurised milk and close to the literature data. Birlouez-Aragon et al. (1998) found 7, Jeanson et al. (1999) 3–10, Villamiel et al. (1999) 6.9–10, Feinberg et al. (2006) 4 and Mayer et al. (2010) 8.1–13.3 mg/100 g protein. A wide range for the FRS contents of UHT market milks appears in the literature. Pellegrino et al. (1995a) estimated 120–230 and 30–110 mg/100 g protein furosine in UHT-IM and UHT-DM milks close to the 35–109 and 108–240 mg/100 g protein found by Van Renterghem and De Block (1996). Elliott et al. (2005) reported 188 ± 51.8 mg/100 g protein for UHT-DM and 371 ± 88.7 mg/100 g protein for UHT-IM milks. Cattaneo et al. (2008) reported 42–206 mg/100 g protein for market UHT-DM milks and Mayer et al. (2010) 93.1–485 mg/100 g protein. On the contrary, Corzo et al. (1994a) reported low


L. Sakkas et al. / Food Chemistry 159 (2014) 293–301

Table 2 Thermal treatment indices of market milks. ND: not detected. LP: low pasteurised. Peroxidase positive. HP: high-pasteurised peroxidase negative. UHT: ultra high temperature. MF + LP: microfiltered and pasteurised. peroxidase positive. FF: full-fat. LF: low-fat. LL: low lactose. Product label _Milk type





a-la c (mg/L)



970 890 858

1306 1358 1376

129 152 123


832 1046

1012 1159

132 119


35 69

116 127

824 674


2514 2583 2280 2821 2617

1709 1701 1669 1861 1456



2621 2831

1401 1464



2774 2657 2520

1663 1697 1655



492 538 624

1073 1071 1195

60 66 64


358 376

865 997

117 100


1645 1680 1682

1474 1595 1607

ND ND 7.8


1908 1822

1322 1415


8_MF + LP/FF

3166 3086 2989

1769 1724 1703


8_MF + LP/FF

3555 3388

1489 1560



1963 1803 1755

1582 1618 1534



1258 1609 1594

1491 1528 1547



1882 2191

1362 1436



267 205 153

838 886 821

68 97 98


2510 2354 2379

1717 1680 1665



256 253 219

873 890 857

136 132 109


417 304 258

1187 1118 1021

52 73 81


471 461

1076 1080

99 82


1759 1672 1693

1584 1553 1586



3434 3168 1254 1153

1840 1790 1470 1332



1071 1144

1033 1056

33 19






FRS-P f (mg/100 g protein)


















10.4 (continued on next page)


L. Sakkas et al. / Food Chemistry 159 (2014) 293–301

Table 2 (continued) Product label _Milk type

a b-f





a-la c (mg/L)







FRS-P f (mg/100 g protein)





1233 1290

1201 1219

76 52




116 118

590 545





374 275

882 875




According to product label. as in Table 1;

amounts of FRS in UHT milks, i.e. 39–53.4 and 15.7–17.8 for UHT-DM and UHT-IM, respectively. The average FRS content of the eleven samples of the category HP was 52.9 ± 73.9 mg/100 g protein or 17.0 ± 23.8 mg/L. The MF + LP milk was similar to LP and TM with respect also to this index. The FRS along with LCT figures confirmed that very variable heating conditions and methods were applied during the production of this category of milks. In five samples with native b-lg >1800 mg/L and no detectable quantities of LCT, FRS was lower than the proposed limit of 20 mg/100 g protein. There are fewer reports about ESL/HP milks in the literature compared to UHT milk. Birlouez-Aragon et al. (1998) found an average FRS content of 11.4 ± 2.35 mg/100 g protein in HP market milks; the data of Villamiel et al. (1999) showed 10.1–31.4 mg FRS per 100 g protein. The most informative study about ESL milk is that of Mayer et al. (2010), who analysed 71 market ESL milks and found FRS contents from 11 to 262.2 mg/100 g protein; the majority of them contained >20 mg FRS per 100 g protein. They report that according to their study an upper limit for FRS corresponding to 1800 mg/L acidsoluble b-Lg for ESL milks would be 40 mg/100 g protein. 4. Conclusion Compilation of the experimental and market milk analyses showed that non-detectable quantities of LCT and FRS

Assessment of heat treatment of various types of milk.

Raw milk (RM), reconstituted condensed milk (CM) and three types of reconstituted milk powders (SMPs) were heated indirectly at 80-140°C for 4 s. Nati...
515KB Sizes 1 Downloads 3 Views