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Keywords:

  • milk;
  • packaging;
  • sensory evaluation;
  • shelf life;
  • ultra-high temperature

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusions
  7. Acknowledgments
  8. References

ABSTRACT:  The objective of this study was to evaluate the sensory stability of ultra-high temperature (UHT) milk subjected to different heat treatments and stored at room temperature in white high density polyethylene bottles (HDPE) pigmented with titanium dioxide. Two lots of 300 units each were processed, respectively, at 135 and 141 °C/10 s using indirect heating and subsequently aseptically filled in an ISO class 7 clean room. These experimental lots were evaluated for appearance, aroma, flavor, and overall appreciation and compared to samples of commercial UHT milk purchased from local commercial stores. The time–temperature combinations investigated did not affect either the acceptability or the shelf life of the milk. Despite the limited light barrier properties of HDPE bottles, the product contained in the package tested exhibited good stability, with a shelf life ranging from 4 to 11 wk. Within this time period, the acceptability of the experimental lots was similar to that of the commercial products. The results achieved in this study contribute to turn the low-cost UHT system investigated into a technically viable option for small-size dairy processing plants.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusions
  7. Acknowledgments
  8. References

UHT milk is the most important dairy product marketed in Brazil, accounting for more than 75% of all legally marketed milk (ABLV 2008). Like other aseptically packaged beverages, such as fruit juices and aqueous soybean extracts, commercially sterile milk (that is, UHT milk) that remains stable at ordinary room temperatures is most commonly packaged in aseptic cartons made of several laminated layers. This seems to be the prevailing market trend all over the world, with the exception of only a few countries, such as Canada and the United States, where pasteurized milk continues to be the most consumed dairy product. Plastic packages, such as bottles—custom-designed or not—constitute a potential option for small-scale dairy processors or those who seek to differentiate their product in the marketplace (Romano and others 1998; Petrus and Faria 2007).

High-density polyethylene (HDPE) is a versatile plastic with many uses, especially for packaging. This plastic, which carries low risk of leaching and is readily recyclable, is commonly used for packaging pasteurized milk and an array of high added value dairy beverages. The main advantages of aseptically filled plastic bottles as compared to laminated cartons include: the possibility of producing the packages on the same premises where the milk is processed; access to a wider choice of suppliers and thus more competitive options; develop custom-made bottles of multiple shapes and sizes, creating an opportunity to build a differentiated brand image; transparent to translucent container walls through which the product in the container can be viewed directly; practical and easy to handle, open, and close. In the particular case of monolayer HDPE, there are additional advantages of low cost and ready recyclability. On the other hand, the drawbacks of plastics materials are their high oxygen permeability and low light barrier properties, which may cause nutritional losses and bring about undesirable changes in the sensory characteristics of the product during storage (Drennan 1983; Nicolas 1995; Romano and others 1998).

The objective of this study was to evaluate the sensory stability of UHT milk subjected to different heat treatments and aseptically filled into white, titanium oxide pigmented high-density polyethylene (HDPE) bottles during storage at room temperature.

Materials and Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusions
  7. Acknowledgments
  8. References

Raw materials

Tests were conducted using pasteurized, homogenized (16 MPa, 13 MPa at the 1st stage, and 3 MPa at the 2nd stage) whole fluid milk as raw material. Milk samples were submitted to the following microbiological and physicochemical tests, performed in triplicate: standard plate counts, mesophilic aerobic sporeforming bacteria counts (Marshall 1993), fat content, titrable acidity, ethanol stability, density, and defatted dry matter (Cunniff 1997).

Packaging

Processed milk was filled into white titanium dioxide (TiO2) pigmented HDPE bottles (500 mL) (Plastirrico Ltda, São Paulo, SP, Brazil), heat-sealed with an aluminum-foil-LDPE laminate and closed with a HDPE screw cap (Plásticos Pirituba Ltda).

Processing and aseptic filling

Production experiments were performed on a pilot scale aseptic filling system developed by Petrus and Faria (2007).

Pasteurized, homogenized whole milk was added with 0.1% sodium citrate to increase heat stability. Thermal processing was accomplished using a plate heat exchanger with a flow capacity of 300 L/h. Two lots were processed at 135 °C/10 s and 2 other lots at 141 °C/10 s. Upon completion of the heat treatment, the product was cooled to 25 °C in approximately 22 s and routed to an aseptic holding tank installed in an ISO class 7 clean room where the milk was kept for 2 h before starting the filling operation.

Prior to filling, the HDPE bottles were sterilized by spraying with a 0.5% peracetic acid solution at 35 °C for 10 s, followed by rinsing with microfiltered water. The screw caps and LDPE-coated aluminum foil seals were sterilized by soaking in this solution for 2 min (Abreu and Faria 2004).

Filling was accomplished in an ISO class 7 clean room. Heat-treated milk was filled using a hand-operated dosing valve and aseptic filling techniques. The headspace was about 50 mL. The bottles were heat sealed with a heat-sealing machine utilizing electromagnetic induction. The product was stored exposed to natural light and at room temperature (22 ± 4 °C).

Physicochemical analyses

Physicochemical characterization of the UHT milk was accomplished by submitting 3 samples of each lot to the following analyses: fat content, total protein, titrable acidity, cryoscopy, density, and defatted dry matter (Cunniff 1997). The basic principles of the above-mentioned analyses are described below.

Fat content H2SO4 is added to a known weight of milk contained in a babcock test bottle. The added H2SO4 produces heat that, in turn, separates the fat, which was subsequently centrifuged. Next, H2O was added and the amount of fat determined in the graduated portion of the babcock bottle. Results were expressed as percent fat by weight.

Total protein Milk was digested in H2SO4 to release nitrogen from protein and retain nitrogen as ammonium salt. Concentrated NaOH was added to release NH3, which was distilled, collected in a H3BO3 solution, and titrated.

Titrable acidity An aliquot of milk added with phenolphthalein was titrated with NaOH.

Cryoscopy A test portion of milk is supercooled to the appropriate temperature and crystallization was induced by mechanical vibration, which causes the temperature to rise quickly to a plateau that corresponds to the freezing point of the sample.

Density (specific gravity) It was determined with lactodensimeter and results expressed at 15 °C.

Defatted dry matter It was determined by indirect method based on specific gravity and fat content values.

Acceptability tests

Sensory stability of the UHT milk lots was estimated on the basis of the results of acceptance tests conducted after 2, 3, 4, 7, 8, 9, 11, and 13 wk nonrefrigerated storage. The sensory panel consistent of 40 habitual consumers of UHT milk. The panelists were asked to describe the sensory attributes of appearance, aroma, flavor, and overall appreciation by assigning a liking score on a 9-point hedonic scale (1 = dislike extremely; 5 = neither like nor dislike; 9 = like extremely) (Stone and Sidel 1993).

The tests were performed in individual booths lighted by a fluorescent white lamp at 10:00 a.m. Approximately 50 mL of milk at a temperature of about 12 °C was poured into plastic cups coded with random 3-digit numbers for identification. Panelists were monadically presented with a maximum of 5 samples per sensory session. Unsalted crackers and mineral water were provided to cleanse the palate. Panelists were offered chocolate as an incentive to participate throughout the entire sensory evaluation process.

The 1st sensory analysis session was conducted 2 wk after processing of the experimental lots, since commercial sterility testing (incubation at 35 °C/10 d) had to be performed prior to sensory evaluation. In this session, panelists were also asked to evaluate 4 samples of commercial UHT milk (products of different brands purchased from local retail outlets, with processing dates ranging from 1 to 2 wk prior to sensory evaluation). One milk brand was taken to serve as control for subsequent tests (ASTM 2005).

Statistical analysis

The results of the acceptance tests were statistically analyzed using analysis of variance (ANOVA) and Tukey's test with significance set a priori at P < 0.05, using the statistical software program Assistat 7.4 beta (Silva, 2007).

Results and Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusions
  7. Acknowledgments
  8. References

Raw material characterization

The results of the microbiological and physicochemical analyses performed on samples of raw material are depicted in Table 1, along with their respective reference values. Pasteurization and cooling prior to UHT processing to enhance the protein stability of the finished product is a common practice in the Brazilian dairy industry. The use of homogenized milk partially compensated for the lack of a homogenizer on the processing line.

Table 1—.  Characterization of raw material (pasteurized, homogenized whole fluid milk).
ParameterRaw milkStandard
1.1x1.2x2.1y2.2y
  1. eDefatted dry matter.

  2. fStandard plate count.

  3. gMesophilic aerobic sporeforming bacteria count.

  4. xRaw material processed at 135 °C/10 s—1° (1.1) and 2° (1.2) trials.

  5. yRaw material processed at 141 °C/10 s—1° (2.1) and 2° (2.2) trials.

Fat (%) 3.6 ± 0.23.6 ± 0.13.6 ± 0.1 3.6 ± 0.1≥3.0a, b
Acidity (°D)19.5 ± 0.217.0 ± 0.3 18.2 ± 0.1 16.5 ± 0.214.0 to 18.0a, b
Ethanol stability
 68%StableStableStableStableStablea, b
 72%StableStableStableStableStablea, b
 74%UnstableStableStableStableStablec
Density (kg/L)1.030 ± 0.0011.030 ± 0.0011.030 ± 0.0011.030 ± 0.0011.028 to 1.034b
DDM (%)e8.6 ± 0.18.5 ± 0.18.4 ± 0.18.2 ± 0.1≥8.2a
SPC (UFC/mL)f2.1 × 1024.7 × 1024.0 × 1025.4 × 102≤8.0 × 104b
MASC (UFC/mL)g1.0 × 1014.0 × 1014.6 × 1012.1 × 101<103d

The levels of fat content, density, and defatted dry matter met the minimum quality requirements laid down in Brazilian legislation (BMALS 1996, 2002). Although all the lots of raw materials met the minimum legal requirement for stability to ethanol, the milk with the highest acidity was not stable at ethanol concentrations greater than 72%. Von Bockelmann and Von Bockelmann (1998) recommend a minimum alcohol stability of 74% to avoid formation of deposits in heat exchangers and product changes during storage (sedimentation, flocculation, and others).

Acidity of lots 1.1 and 2.1 did not comply with the product identity and quality criteria for this product category (BMALS 1996, 2002). Considering the limited increase in acidity, samples of these lots were tested to determine their correlation with shelf life and the importance of the raw material quality for milk packed in polyethylene bottles.

Although all the experimental lots exhibited similar standard plate counts and mesophilic aerobic sporeforming bacteria counts, the differences in acidity and, consequently, in ethanol stability, showed that each lot had its own microbiological profile. These possible distinct microbial profiles may be associated with the natural variability of the raw material and contaminations that occur during milking, handling, storage, transportation, and processing (Kessler 1981; Von Bockelmann and Von Bockelmann 1998).

Physicochemical evaluation

The results of the physicochemical characterization analyses are shown in Table 2. All the lots complied with the requirements for fat, protein, and defatted dry matter contents (BMALS 1996, 2002). The acidity level of the product fell within the same range as that of the raw material (Table 1).

Table 2—.  Physicochemical characterization of UHT milk.
ParameterExperimental trialStandard
1.1x1.2x2.1y2.2y
  1. cDefatted dry matter.

  2. xMilk 135 °C/10 s – 1° (1.1) and 2° (1.2) trials.

  3. yMilk 141 °C/10 s – 1° (2.1) and 2° (2.2) trials.

Fat (%)3.5 ± 0.13.5 ± 0.13.5 ± 0.13.6 ± 0.1≥3.0a
Protein (%)3.5 ± 0.13.3 ± 0.13.3 ± 0.13.3 ± 0.1≥2.9b
Acidity (°D)18.8 ± 0.3 17.1 ± 0.1 18.1 ± 0.1 16.9 ± 0.1   14.0 to 18.0a
Cryoscopy (°H)−0.550 ± 0.001  −0.550 ± 0.001  −0.550 ± 0.001  −0.550 ± 0.001    ≤−0.530b
Density (kg/L)1.031 ± 0.0011.032 ± 0.0011.031 ± 0.0011.031 ± 0.0011.028 to 1.034b
DDM (%)c8.7 ± 0.38.3 ± 0.28.2 ± 0.18.6 ± 0.1≥8.2a

Sensory analysis

Comparison between experimental and commercial samples after 2 wk storage The average acceptability ratings obtained using the 9-point hedonic scale for each of the 4 samples of experimental UHT milk and 4 samples of commercial brands after 2 wk storage at room temperature are shown in Table 3, along with the percentage of consumers that approved the sample by assigning a rating ≥ 6.0.

Table 3—.  Consumer sensory acceptance of samples of UHT milk and commercial samples after 2 wk storage at room temperature.
MilkTrialAverage ratingsa/Approval (%)b
AppearanceAromaFlavorOverall appreciation
  1. aMeans followed by the same character are not statistically different (P > 0.05), on a 9-point hedonic scale (1 = dislike extremely; 5 = neither like nor dislike; 9 = like extremely).

  2. bPercentage of consumers that assigned ratings of liking ≥ 6.0.

135 °C/10 s17.3 ab/876.0 a/536.3 a/736.5 a/90
27.1 ab/936.6 a/736.7 a/736.8 a/90
141 °C/10 s1 7.3 ab/1006.6 a/676.3 a/736.4 a/90
26.7 b/77 6.2 a/576.1 a/736.1 a/90
CommercialA7.3 ab/906.8 a/736.5 a/736.9 a/90
B7.7 a/97 6.4 a/736.3 a/736.6 a/90
C7.6 ab/936.6 a/706.4 a/736.6 a/90
D8.0 a/90 6.5 a/776.3 a/736.7 a/90

In this study, the milk samples were subjected to sensory evaluation after the 1st week of storage, due to the need to previously verify the commercial sterility of the experimental lots. It should be noted that enhanced consumer acceptability is observed after 1 wk storage as a result of a reduction in the intensity of its “cooked” flavor (Shipe and others 1978; Hostettler 1981).

The ratings for the attributes aroma, flavor, and overall appreciation were not significantly different at the P > 0.05 level and received an average score in the 6 to 7 range, somewhat between “like slightly” and “like moderately.” The appearance of the sample processed at 141 °C/10 s in the 2° trial, although it received ratings that did not statistically (P > 0.05) differ from those received by the other experimental samples and commercial samples “A” and “C,” scored lower than the commercial samples “B” and “D.” For the most part, the rating of approval for all sensory attributes was above 70%. The high approval ratings in the same order of magnitude received by the experimental and the commercial UHT milk samples were corroborated by the results of overall appreciation assessment, in which 90% of the panelists assigned ratings ≥ 6.0. Furthermore, the intensity of the heat treatment applied did not influence the acceptance scores of the samples.

Commercial sample A was taken as control for subsequent sensory tests. The acceptability ratings of this product were not significantly different (P > 0.05) from those received by the experimental samples (ASTM 2005).

Evaluation of sensory stability

The results of the sensory acceptance tests using the 9-point hedonic scale of the experimental samples and control (different lots of brand A milk, with processing dates ranging from 1 to 2 wk prior to sensory evaluation sessions), from the 4th week of storage onwards are presented in Tables 4 to 7. Data from the 3rd and 11th wk of storage are not shown because they were not statistically different (P > 0.05) from the previous evaluation session.

Table 4—.  Consumer acceptance of appearance of UHT milk samples stored at room temperature.
MilkTrialMeansa/Approval (%)b
4th wk7th wk8th wk9th wk13th wk
  1. aMeans followed by the same lowercase letter within columns (comparison between heat treatments) or by the same uppercase letter within rows (comparison between storage times) are not statistically different (P > 0.05), on a 9-point hedonic scale (1 = dislike extremely; 5 = neither like nor dislike; 9 = like extremely).

  2. bPercentage of consumers that assigned ratings ≥ 6.0.

  3. cDifferent lots of brand A milk, with processing dates ranging from 1 to 2 wk prior to sensory assessment.

  4. dND = not determined, due to end of shelf life (average ratings < 6.0 and percentage of approval < 60%, for at least one of the sensory attributes assessed in the preceding sensory evaluation session).

135 °C/10 s1 8.0 a A/1006.8 a A/805.0 b B/50NDND
27.6 a A/906.7 a A/737.5 a A/906.6 a A/736.7 a A/83
141 °C/10 s17.3 a A/904.2 b B/37NDdNDND
2 7.6 a AB/90 6.7 a AB/80 7.3 a AB/876.5 a B/70ND
Controlc 7.7 a A/90 8.0 a A/1008.1 a A/977.9 b A/937.9 b A/97
Table 5—.  Consumer acceptance of aroma of UHT milk samples stored at room temperature.
MilkTrialMeansa/Approval (%)b
4th wk7th wk8th wk9th wk13th wk
  1. aMeans followed by the same lowercase letter within columns (comparison between heat treatments) or by the same uppercase letter within rows (comparison between storage times) are not statistically different (P > 0.05), on a 9-point hedonic scale (1 = dislike extremely; 5 = neither like nor dislike; 9 = like extremely).

  2. bPercentage of consumers that assigned ratings ≥ 6.0.

  3. cDifferent lots of brand A milk, with processing dates ranging from 1 to 2 wk prior to sensory assessment.

  4. dND = not determined, due to end of shelf life (average ratings < 6.0 and percentage of approval < 60%, for at least one of the sensory attributes assessed in the preceding sensory evaluation session).

135 °C/10 s16.8 a A/806.3 ab A/636.4 a A/57NDND
26.7 a A/706.7 a AB/67 6.6 a AB/73 6.4 a AB/705.5 a B/47
141 °C/10 s1 6.1 a AB/605.7 b B/43 NDdNDND
26.3 a A/636.8 a A/63 6.7 a A/736.3 a A/63ND
Controlc 6.7 a A/736.6 a A/67 7.0 a A/836.6 a A/676.7 b A/70
Table 6—.  Consumer acceptance of flavor of UHT milk samples stored at room temperature.
MilkTrialMeansa/Approval (%)b
4th wk7th wk8th wk9th wk13th wk
  1. aMeans followed by the same lowercase letter within columns (comparison between heat treatments) or by the same uppercase letter within rows (comparison between storage times) are not statistically different (P > 0.05), on a 9-point hedonic scale (1 = dislike extremely; 5 = neither like nor dislike; 9 = like extremely).

  2. bPercentage of consumers that assigned ratings ≥ 6.0.

  3. cDifferent lots of brand A milk, with processing dates ranging from 1 to 2 wk prior to sensory assessment.

  4. dND = not determined, due to end of shelf life (average ratings < 6.0 and percentage of approval < 60%, for at least one of the sensory attributes assessed in the preceding sensory evaluation session).

135 °C/10 s16.8 ab A/707.0 a A/806.6 a A/73NDND
27.4 a A/87 6.6 a A/807.3 a A/90 6.4 ab A/773.7 a B/30
141 °C/10 s16.0 b AB/574.6 b B/43NDdNDND
2 6.6 ab AB/807.3 a A/80 6.7 a AB/775.7 a B/57ND
Controlc 7.1 ab A/907.3 a A/837.5 a A/877.1 b A/877.3 b A/90
Table 7—.  Consumer acceptance of overall appreciation of UHT samples stored at room temperature.
MilkTrialMeansa/Approval (%)b
4th wk7th wk8th wk9th wk13th wk
  1. aMeans followed by the same lowercase letter within columns (comparison between heat treatments) or by the same uppercase letter within rows (comparison between storage times) are not statistically different (P > 0.05), on a 9-point hedonic scale (1 = dislike extremely; 5 = neither like nor dislike; 9 = like extremely).

  2. bPercentage of consumers that assigned ratings ≥ 6.0.

  3. cDifferent lots of brand A milk, with processing dates ranging from 1 to 2 wk prior to sensory assessment.

  4. dND = not determined, due to end of shelf life (average ratings < 6.0 and percentage of approval < 60%, for at least one of the sensory attributes assessed in the preceding sensory evaluation session).

135 °C/10 s17.1 a A/83 7.0 a A/806.2 a A/60NDND
27.2 a A/87 6.6 a A/80 7.1 ab A/93 6.4 ab A/774.1 a B/33
141 °C/10 s16.0 b A/63 4.1 b B/33NDdNDND
2 6.7 ab AB/80 6.8 a AB/77 6.8 a AB/775.8 a B/50ND
Controlc 7.3 a A/93 7.3 a A/837.6 b A/977.2 b A/877.4 b A/90

In the 4th wk of storage, the results obtained were similar to those of the previous week, except for the sample processed at 141 °C/10 s in the 1st trial. This product presented average ratings for flavor (Table 6) and overall appreciation (Table 7) within in the limits of sensory acceptance and shelf life (6 =“like slightly”), different from the ratings assigned to the control and other samples (P < 0.05) for overall appreciation. The approval percentages of the product were close to 60% for aroma, flavor, and overall appreciation.

The main change in appearance of the experimental UHT milk samples reported and commented upon by the panelists concerns partial separation of fat, a phenomenon related the effect of the homogenization the pasteurized milk was subjected to before UHT processing at a pressure lower than the minimum pressure required for the production of long-life milk (20 to 25 MP, 15 to 20 MP at the 1st stage, and about 5 MPa at the 2nd stage [Von Bockelmann and Von Bockelmann 1998]).

From the 4th wk of storage onwards, sensory quality of the experimental samples began to deteriorate and determined the end of shelf life. The average ratings for the sensory attributes evaluated fell below 6 (within the range between the hedonic scale values of the categories “dislike extremely” and “like slightly”), while approval percentages (that is, the percentages of consumers that assigned a rating score ≥ 6) were below 60%, both of which had been previously established as criteria to discontinue sensory evaluation sessions and, hence, determine the end of sensory shelf life.

In the 7th wk, all sensory attributes of the sample processed at 141 °C/10 s in the 1st trial were below the acceptance criteria and were significantly different (P < 0.05) from the control and other experimental UHT samples. Since the product had not been submitted to sensory assessment in the 5th and 6th wk of storage, its shelf life was estimated at 4 wk.

By the 8th wk of storage, the sample processed at 135 °C/10 s in the 1st trial had exceeded its shelf life as a result of a significant and substantial reduction in the acceptability scores for appearance. Consequently, the shelf life of the product was estimated at 7 wk.

Ratings below the threshold values for flavor and overall appreciation assigned in the sensory assessment session carried out after 9 wk storage determined the end of shelf life of the UHT milk sample processed at 141 °C/10 s in the 2nd trial. Based on that, the shelf life of this product was estimated at 8 wk.

The sample processed at 135 °C/10 s in the 2nd trial reached the end of its shelf life after 13 wk storage at room temperature and differed from the control sample (P < 0.05) for all sensory attributes, leading to an estimated shelf life of 11 wk.

Sensory stability of the 135 °C/10 s samples varied from 7 to 11 wk, considerably different from the samples processed at 141 °C/10 s which exhibited a 4 to 9 wk shelf life. The samples with the shortest shelf life had been produced from raw materials with high acidity levels, as shown in Table 1. The variation observed in the shelf life of the products may also be associated with the microbiological profile of the raw materials used, and, consequently, biochemical reactions caused by the activity of microbial enzymes (Kessler 1981; Von Bockelmann and Von Bockelmann 1998). These factors may have masked or cancelled a possible distinct effect of the heating treatments studied on the sensory acceptability and shelf life of UHT milk. Apparently, the intensity of the heat treatment did not affect the sensory stability of UHT milk. This finding is in accordance with results reported by Hansen and others (1974) who observed that milk processed at 135 °C/10 s and 143 °C/10 s, by direct heating, did not develop any significant difference in their sensory attributes throughout 30 d storage at 7.2 °C.

The shelf life of commercial UHT milk in conventional aseptic milk cartons varies from 3 to 6 mo (Von Bockelmann and Von Bockelmann 1998; ABLV 2008). It is expected that storage time has a significant effect on the sensory quality of UHT milk packaged in plastic bottles because of their lower barrier properties (Nicolas 1995; Romano and others 1998). However, it was found that the products' sensory attribute ratings and their percentages of approval remained high and relatively constant up to the end of sensory shelf life, witch varied from 1 to almost 3 mo. During this storage time, the experimental samples practically did not differ from the control. They differed only when the average sensory attribute ratings of the experimental samples fell below 6 and their approval percentages were < 60%, evidencing the appropriateness of these criteria to determine the end of sensory shelf life.

Conclusions

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusions
  7. Acknowledgments
  8. References

UHT milk packaged in TiO2 pigmented HDPE and stored at room temperature showed considerable variations in shelf life—varying between 4 and 11 wk—associated with the variability of the raw material used. Heat treatment did not affect either sensory acceptance or shelf life of the product. In spite of the limited light barrier properties of the bottle used to hold UHT milk, the product in this type of plastic package exhibited good stability and obtained sensory acceptability ratings similar to those assigned to commercial products before the end of sensory shelf life. Within this context, the system investigated was found to constitute a technologically viable and low-cost option for dairy processing plants that distribute their products within a limited radius.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusions
  7. Acknowledgments
  8. References

The authors gratefully acknowledge the support of the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP).

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusions
  7. Acknowledgments
  8. References
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