MATERIALS AND METHODS

Study area: The research was conducted at the Manoko Experimental Station of Indonesia Spices and Medicinal Crops Research Institute at Lembang, West Java, Indonesia. The location of the research station is 60°48'30.75" South Latitude, 107°36'50.68" East Longitude and 1,264 m above sea level. The average annual maximum temperature in Lembang is 28°C, while the average annual minimum temperature is 19°C. The research started in early 2021 for the preparation of animals and Citronella distillation waste biomass. The experiments and data collection were conducted in April, 2021.

Animals: The methods did not generate stress and discomfort for the animals. Therefore, no animals were harmed during the study. The study was conducted on 10 Friesian Holstein (FH) cows. Each cow was fed with 40 kg/head/day of solid Citronella distillation waste biomass at 8 am (20 kg/head/day) and 5 pm (20 kg/head/day). The Citronella feeding replaces Elephant grass (Pennisetum purpureum) as a source of forage. The Citronella feeding was conducted for ten days before the milk test was taken. The cows were still given local sources of concentrate feed and formulated concentrate feed from North Bandung Milk Association in addition to forage.

Milk sampling: A sampling of fresh milk was carried out in the morning according to the milking time at intervals of 5.00-6.30 am. The samples were taken compositely on all treated cows and were accommodated in a reservoir bucket, then filtered using a filter cloth. Total filtered milk was put into a special thermos for storing fresh milk for further testing of physical quality, proximate analysis, microbial contamination and heavy metals. The test was conducted at the Bogor Animal Product Quality Testing and Certification Centre.

Milk analysis: The test result was compared with the raw milk quality of the Indonesian National Standard/Standar Nasional Indonesia (SNI) that has been regulated in SNI 3141.1:2011¹⁰ (Table 1). The milk quality can determine the incentive level of the premium price¹¹. In addition, the test result was also compared with European Union (EU) standard (Table 2). Milk requirement for the EU follows regulations EC 852/2004 and 853/2004 as a replacement for directive 92/46/EEC¹². Physical testing includes colour, taste, odour, alcohol test and degree of acidity (pH). The proximate analysis consisted of testing for total solid (%), fat (%), protein (%) and lactose (%). Tests for microbial contamination include total plate count (TPC), E. coli, Coliform, Salmonella sp. and S. aureus. Heavy metal testing includes lead (Pb), mercury (Hg) and Arsenic (As).

Statistical analysis: The physical characteristics test used qualitative analysis. Panellists were involved in this test. The proximate test, heavy metals testing and microbial contamination assessment followed standard lab protocols. Descriptive statistics were used to present the lab result.

RESULTS AND DISCUSSION

Nutrition of Citronella waste biomass: Based on previous studies, the nutrition of Citronella waste biomass can be seen in Table 3. The protein content of Citronella waste (7.00%) was higher than that of straw (4.00%). The crude fibre content in Citronella waste was 25.73%, lower than elephant grass and straw, 34.17 and 32.14%, respectively. Meanwhile, the energy content of Citronella waste is 3,353 kcal kg^–1, higher than rice straw with a value of 3,167 kcal kg^–1.

The availability of quantity protein will change the ratio of carbohydrates fermentability. It is directly related to the microbial biomass in the rumen¹⁵. In general, feed protein sources are more expensive than feed energy sources. The higher the protein contained, the better the quality of the forage. Therefore, it is necessary to find alternative protein sources that have the same quality as concentrate sources but are affordable to farmers. The main source of protein is usually from the Leguminous family¹⁶. Suboptimal availability and utilization of Citronella distillation waste allow it to be further formulated as forage.

Physical and proximate test: Expert panellists conduct physical testing visually to distinguish the colour, taste and viscosity of the milk. The observations showed no significant change in milk quality produced from cows fed with Citronella waste compared with other forage. The appearance of milk was a uniform light cream natural colour. It has a sweet taste and a fairly desirable flavour. The alcohol clotting test shows a negative value (normal) or no alcohol formation from the resulting milk. It means there is no alcohol from microbial fermentation due to contamination. Therefore, it meets a standard requirement.

Finally, the degree of acidity (pH) obtained was 6.8. The current finding for pH was slightly higher than previous research Beni Mellal Region (6.7)¹⁷. However, it is still in the tolerable range of neutral pH, namely 6.3-6.8 of the Indonesian National Standard. The milk-specific gravity was 1.028, slightly above the normal level (1.027). It was better than a previous study of the quality of raw milk in smallholder farmers conducted by Gwandu et al.¹⁸. Physically, the produced milk is still acceptable to buyers.

The results of the proximate test of cow milk produced from the feed of distilled Citronella were shown in Fig. 1. The test results for the parameters indicated that they were above the quality standard set by Indonesian National Standard¹⁰.

Total solid is one of the main determining factors of price level on milk quality¹¹. The total solid result was 11.7%, higher than the minimum standard point (7.8%). The protein content of raw milk shows the milk quality. The higher the protein and fat content, the higher the quality of fresh milk. The content of fresh milk was the main requirement for standard raw materials to be further processed into other value-added products. According to Jørgensen et al.¹⁹, consumer interest in high-protein yoghurt has grown, in part due to advancements in flavour and texture. The higher the milk protein content, the better the quality of the yoghurt.

The high-fat, protein and lactose content indicate the large amount of total energy produced from fresh milk. Compared to the other study conducted by Harjanti and Sambodho²⁰, lactose contains 3.36% and the Indonesian National Standard¹⁰ is 4%. It means the lactose contained in this research was higher than the Indonesian National Standard¹⁰ and previous studies²⁰.

In addition, the contained essential oil could improve the quality of digestion. Benchaar et al.²¹ stated that essential oil prospectus improves nutrient digestion efficiency and reduces adverse environmental impact. Furthermore, according to Mishra et al.²², essential oil was a good additive to dairy products, especially for bio-preservative, antioxidant, anti-microbial activities and improving the flavour of the milk.

Microbial contamination level: The results of the microbial contamination test on the milk samples tested were presented in Table 4. The total plate count (TPC) of the milk samples produced by cows fed with Citronella distillation waste feed was slightly higher than the standards set in Indonesian National Standard¹⁰. It needs attention to improve the way of feeding, the sanitation of the cage and the process of milking the cows.

The microbial contamination contained in fresh milk shows its quality. The microbes, in general, will affect the shelf life and speed of deterioration of milk before it is processed into other products. According to the Center for Food Safety and Food Standards Australia, the total plate count of bacteria in milk ranges from 105 to 107 CFU mL^{–1 23}. The satisfactory category of milk has a TPC of less than 105 CFU mL^–1 and the unsatisfactory had a TPC greater than 107 CFU mL^{–1 23}. It means the maximum microbial contamination was still in the appropriate range. Improvements in sanitation can significantly reduce the acidity level from 0.19-0.14% and reduce the number of bacteria²⁴.

The high total TPC is usually caused by the lack of sanitation management of the cage. The low amount of TPC in fresh milk may be due to the good pattern of sanitation, cage cleaning, or sanitation of the cage environment^25,26. Milk that has been exposed to excessive levels of microbial contamination is contaminated with bacteria and cannot be sold to consumers. The TPC levels may be impacted by several aspects of pasteurized milk production²⁷. The high levels of microbes were related to increased enzyme activity, resulting in milk and derivative product defects²⁸. In addition, raw milk was not contaminated by Staphylococcus aureus and Enterobacteriaceae. They are microbes related to human gastroenteritis poisoning and the microbial indicators of hygiene practices and food quality^29-31.

Fig. 1:

Proximate levels of raw milk quality from cows fed with Citronella distillation waste biomass

Heavy metal content: The test results on heavy metal contamination showed that the lead (Pb) value of 0.015 μg mL^–1 was less than the Indonesian National Standard threshold set at 0.02 μg mL^–1 and a previous study was conducted in Turkey³². Meanwhile, mercury (Hg) and arsenic (As) were not detected. Thus, the safety level of fresh milk from cows fed with Citronella distillation waste still meets the established standards.

Citronella distillation waste is a by-product of agriculture, using inputs from fertilizers. It can be exposed to fossil fuel burning or mechanization. The potential risk of heavy metal toxicity in raw milk can be contaminated by environmental pollution and water disposal on the irrigated farm^33-35. The use of fuel oil containing lead in tractor engines and agricultural vehicles is feared to accumulate in digested forage. Heavy metal contamination can also be obtained from the irrigation system if the water used for cultivation comes from industrial waste.

In this study, preliminary information on the potential of Citronella waste feeding as an alternative forage without lowering the milk quality was provided. This study only compared the milk quality with the national and international standard which make it a limitation of this study. Therefore, further research is needed on milk quality comparison between Citronella waste feeding and forage feeding.

CONCLUSION

The milk quality from dairy cows fed with Citronella distillation waste biomass met the Indonesian National Standard (SNI) for visual tests, proximate analysis, microbial contamination and heavy metal content. The test results showed protein content of 3.16% (SNI 2.8%), fat 5.38% (SNI 3.0%) and lactose 4.63%. Heavy metal testing showed no mercury (Hg) and arsenic (As), while lead (Pb) was 0.01 g mL^–1 below SNI (0.02 g mL^–1). In addition, no microbial contamination was detected for Staphylococcus aureus and Enterobacteriaceae. It means that Citronella by-product biomass can be used for alternative forage and does not decrease milk quality.

SIGNIFICANCE STATEMENT

This preliminary study discovered that Citronella distillation waste biomass can be used as forage for dairy cow feed. The milk from cows that fed with Citronella distillation waste biomass met the national standard on physical characteristics and nutritional contents. The milk also passed the heavy metals testing and microbial contamination assessment. This preliminary information will help the researchers to discover other benefits of the Citronella distillation waste biomass as the basis of further research on feed formulation, milk productivity, digestibility, enteric methane emission and comparison with other forages. Distillers produced waste biomass can initiate the utilisation of by-products as added value and promote a circular economy of zero waste concept.

ACKNOWLEDGMENTS

We thank the Indonesian Agency for Agricultural Research Development for providing research funding (SP DIPA 018-092.237306/2021). We also would like to express our gratitude to all technicians at Manoko Experimental Station. We also thank the Animal Product Quality Testing and Certification Center, Bogor, for supporting this research.