Joining is your friend

private String transformCsvRowOld(String csvRow) {
    if (StringUtils.isEmpty(csvRow)) {
        return "";
    }

    String tempCsvRow = csvRow.replaceAll("\"", "");
    String[] csvRowFields = tempCsvRow.split("\t");

    String transformedCsvRow = "";
    boolean firstItem = true;
    for (String field : csvRowFields) {
        transformedCsvRow = transformedCsvRow + (firstItem ? "" : ";") + "=\"" + field + "\"";
        firstItem = false;
    }

    return transformedCsvRow;
}

private String transformCsvRowNew(String csvRow) {
    if (StringUtils.isEmpty(csvRow)) {
        return "";
    }

    List<String> csvRowFields = Arrays.asList(csvRow.replaceAll("\"", "").split("\t"));
    return csvRowFields.stream()
            .map(field -> "=\"" + field + "\"")
            .collect(joining(";"));
}